Microminiature hard disk drive

ABSTRACT

Disclosed is a disk drive information storage device which includes a disk for recording and reproducing information, the disk drive information storage device utilizing a rotary actuator, with the rotary actuator including a load beam for supporting a read/write recording element above a surface of the disk. The load beam includes at its outermost end a lift tab, with the lift tab being positioned such that a centerline of the lift tab is offset from a centerline of the load beam. The lift tab cooperates with a cam assembly to provide a dynamic head loading disk drive. The cam assembly is supported by the housing of the disk drive information storage device at a position adjacent to the edge of the disk and adjacent to the lift tab. The cam assembly in cooperation with the lift tab provides a lifting force along the centerline of the load beam. In one embodiment, the above-described dynamic head loading information storage device is provided in a housing having a footprint that includes a first dimension of about thirty-five millimeters. In another embodiment, the disk in the disk drive information storage device has a diameter in the range of from about thirty-three millimeters to about thirty-four millimeters.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to rigid disk drives, and moreparticularly to rigid disk drives for pocket, palm-top, and laptopcomputers.

2. Description of Prior Art

The continuing trend toward smaller portable computers has created theneed for a new class of miniature information storage devices. Portableapplications for information storage devices have resulted inincreasingly severe environmental and physical requirements. Small size,low power consumption, environmental endurance, low cost and lightweight are characteristics that must co-exist in these applications;they cannot be met by simple extensions of previous technology.

Many examples of miniaturized reduced "footprint" disk drives have beendescribed in patents such as U.S. Pat. No. 4,568,988 to McGinley, et al,issued Feb. 4, 1986, Reexamination Certificate (953rd), U.S. Pat. No.B14,568,988, certificate issued Nov. 29, 1988, U.S. Pat. No. 4,933,785,issued Jun. 12, 1990 to Morehouse, et al. The rigid magnetic recordingdisk utilized in the device, described in McGinley, et al., had adiameter of approximately 3.5 inches. In the Morehouse, et al. devicedescribed in that patent, the rigid disks utilized in the drive had anominal diameter of 2.5 inches. The "footprint" (width by lengthmeasurement) of the drive described in the above-noted Morehouse, et al.patent was described as being 2.8 inches by 4.3 inches. That is, thehousing used to enclose the rigid disk drive was 2.8 inches wide and 4.3inches long. A rigid disk drive of that size is generally applicable tocomputers having a size of 8.5 inches by 11 inches by 1 inch. Anotherpatent describing a relatively small diameter disk was issued Jun. 18,1991 to Stefansky, U.S. Pat. No. 5,025,335. Stefansky describes a 21/2'form factor disk drive utilizing a single rigid disk having a diameterof approximately 2.6 inches. However, these products do not provide thecombination of features needed for "pocket,""palm-top" and laptopcomputers.

History has shown that as disk drives become smaller and more efficient,new applications and uses for disk storage become practical. Forexample, using the disk drive as a circuit board assembly componentrequires further reduction in the physical size of the storage device aswell as unique mounting strategies, issues addressed by this invention.

Use of disk drive storage devices in palm-top computers and smallelectronic devices, such as removable font cartridges for laserprinters, require a level of vibration and shock resistance unobtainablewith present large disk drives. These new applications require equipmentto survive frequent drop cycles that result in unusually highacceleration and shock. It is well known that the force on an object isdirectly proportional to its mass, therefore reducing mass is anessential strategy for improving shock resistance.

Portable equipment also makes stringent demands on the durability andstability of the storage equipment under extreme dynamic, static,temperature and humidity stress. A device of small dimensions by itsnature experiences less absolute temperature induced physicaldimensional displacements. High humidity, especially during storageconditions, can aggravate a phenomenon known as "stiction" that occurswith conventional disk drives; the transducer head clings to the smoothdisk surface, which can stall the spin motor and damage the heads.

The greater the power consumption, the larger and heavier the batterypack becomes. Hence, for a given operating time, power consumption is aprimary and unavoidable design consideration for portable devices. Infact, the weight of a portable device is dependent on the total energyrequired to meet operational mission time. For disk drive equipmentenergy use is especially important during what is known as standby orpower-down modes. Low power consumption also reduces parasitic heat, animportant consideration in compact electrical equipment. Reducing thediameter and thickness of the information disk(s) can also providesignificant reduction in power consumption during spin up. Modern diskdrive power management methods use intelligent decision strategies,evaluating disk drive usage patterns to sequence power saving shut downfeatures.

FIG. 24A is a block diagram of a prior art servo field 2400. The servofield 100 is the same length and includes, starting at its leading edge,a write splice sub-field 2401, an automatic gain control (AGC) sub-field2402, a sector mark subfield 2403, an index sector identifier 2404, adefect bit 2405, a Gray code track number sub-field 2406, and a trackposition sub-field 2407 followed by another write splice sub-field.Servo field 2400 is preceded and followed by data regions 2410 and 2411,respectively. As explained more completely below, AGC sub-field 2402 isactually divided into two parts. The first part is a write-to-readtransition zone and the second part provides the actual AGC data.

FIG. 24B is a flat view of the magnetic dibits in one servo field intracks 3 to 6 of the disk. The other servo fields and data fields havethe same general structure as illustrated by the block diagram of FIG.24A. FIG. 24C is the signal pattern generated when the information intrack 3 is read.

FIGS. 49A and 49B illustrate two- and three-disk embodiments of HDAsincorporating the prior art low-profile architecture. The spacingbetween adjacent disks 4920 is approximately two times the space trequired for a read/write read, or 3.0 mm, to provide space for the tworead/write heads 4930 and 4931 disposed between the adjacent disks.Thus, each additional disk 4920 increases the thickness of the prior artHDA by 3.6 mm (two spaces t and 0.6 mm for the thickness of theadditional disk). Therefore, the thickness of the two-disk, four-headHDA of FIG. 49A is approximately 17.2 mm, and the thickness of thethree-disk, six-head HDA of FIG. 49B is approximately 20.8 mm. Ferriteshields 4940 are illustrated in both FIGS. 49A and 49B.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a rigid disk drivehaving reduced physical dimensions, but retaining the storage capacityof larger disk drives, with minimized power consumption and providingextreme resistance to shock and vibration.

A further object of the invention is to provide a disk drive having a 11/4 inch form factor. In accordance with the invention, a rigid diskdrive information storage device is provided which has a base and cover,utilizes one or more information storage disks having a diameter ofapproximately 33.5 mm (1 1/4 inches) provides an information storagecapacity of at least 20 Megabytes.

A disk drive in accordance with one embodiment of the present inventionhas a length of approximately 51 mm, a width of approximately 35 mm anda height of approximately 10 mm in a stacked configuration with anassociated printed circuit board positioned beneath the disk drive.Included is a disk spin motor internal to the housing, and a rotaryactuator for positioning read/write transducer elements over the surfaceof the disk for the recording and play-back of digital information.

In accordance with another feature of the invention, in one embodimentthe transducer support arm of the disk storage device includes a lifttab which, when operated with a cam, provides a means to load or unloadthe head from the spinning surface of the recording disk as described incopending, commonly assigned U.S. patent application Ser. No. 07/629,957filed Dec. 19, 1990 by James H. Morehouse et al., entitled "Rigid DiskDrive with Dynamic Head Loading Apparatus", which is incorporated hereinby reference in its entirety. In addition, a small form factor diskdrive may not be able to produce enough torque to overcome stictionbecause of the low supply voltage and miniature spin motor component,thus making it impossible to start the disk rotating. Otherconfigurations may use conventional contact start-stop head/diskinterface methods.

In accordance with yet another feature of the invention, the disk driveincludes sampled servo fields pre-recorded on each data track of thedisk, which when read back uniquely determine track position and addressinformation as disclosed in U.S. patent application Ser. No. 07/630,475,filed Dec. 19, 1990 by John H. Blagaila et al. entitled "Servo FieldScheme For High Sampling Rate and Reduced Overhead Embedded Servo Systemin Disk Drives", and assigned to the assignee of present invention andincorporated herein by reference in its entirety. Further, the diskdrive in accordance with the present invention incorporates improvementsdisclosed in co-pending, commonly assigned U.S. patent application(SERVO II) Ser. No. 07/765,348 filed on Sep. 25, 1991 by Stephen Cowenentitled "Embedded Servo System With Reduced Overhead" which serves toincrease the number of track following and spin motor servo sampleswhich may be taken per unit time, while allowing increased informationstorage on a track without increased format overhead. The Cowenapplication is incorporated herein by reference in its entirety.

A further object of the invention is to incorporate an improved trackfollowing servo system to minimize the effect of mechanical resonanceswhile permitting very high track densities. This servo system, which isdescribed in copending and commonly assigned U.S. patent applicationSer. No. 07/766,478, filed Sep. 25, 1991, by Thomas B. Andrews entitled"Adaptive Runout Compensation for Miniature Disk Drives", incorporatesfeed-forward run-out compensation by microprocessor control. Thisapplication is incorporated by reference herein in its entirety.

A further object of the invention is to provide a rigid disk storagesystem which includes an inertia actuated latch mechanism to prevent theactuator and magnetic transducers from being moved from their parkedposition resulting from subjecting the disk drive to severenon-operating shocks in the plane of the disk. The inertially operatedlatch described in copending, commonly assigned U.S. patent applicationSer. No. 07/629,929, filed Dec. 19, 1990, by James H. Morehouse et al.,entitled "Rotary Inertial Latch for Disk Drive Actuator now U.S. Pat.No. 5,189,576 issued Aug. 21, 1992," or the latch described and claimedin copending, commonly assigned U.S. patent application Ser. No.07/765,353, filed Sep. 25, 1991, by James H. Morehouse et al., entitled"Rotary Inertial Latch for Disk Drive Actuator", may be utilized. Bothof the foregoing applications we hereby incorporated by reference intheir entirety.

In accordance with yet another feature of the present invention, thedisk drive apparatus has a spin motor which includes a stator having aplurality of windings and a rotor having a plurality of magnetic poles.Stator windings consist of two types, a first type for normal running ofthe motor and a second winding type used during starting to increasetorque and further used during power down sequencing to act as anelectromotive force generator providing power to the rotary actuator tounload the transducer elements from the disk surface. When a disk driveoperates in a continuous start stop configuration, the electromotiveforce may be used to park the heads in the landing zone and providerapid electrodynamic braking of the spin motor to reduce wear and damageto the head disk interface. This feature is disclosed in copending,commonly assigned U.S. patent application Ser. No. 07/630,110, filedDec. 19, 1990, by James H. Morehouse et al , entitled "Spin Motor For AHard Disk Assembly", which is incorporated herein in its entirety. Analternative spin motor is described hereinafter in detail.

A further object of the present invention is to provide a disk drivewith a spin motor control system that includes a back electromotiveforce commutation circuit using digital techniques to generatecommutation pulses, a start up circuit for starting the spin motor, anda monitor circuit for determining the motor spin direction and makingcorrections of direction if necessary after a commutation occurs. Thespin motor control system preferred for use with the disk drive systemdescribed herein is described in copending, commonly assigned U.S.patent application Ser. No. 07/630,470, filed Dec. 19, 1990 by MichaelR. Utenick et al., entitled "Spin Motor Control System for a Hard DiskAssembly", which is incorporated herein by reference in its entirety.

Yet another object of the present invention is to provide methods toreduce errors caused by spin motor induced electromagnetic highfrequency noise that causes interference with track position sampleddata and read back signals.

A further object of the present invention is to provide a low profilerigid disk drive having higher storage capacity per volume of thehousing than previously available. This feature is disclosed incopending, commonly assigned U.S. patent application Ser. No.07/765,352, filed Sep. 25, 1991, by James H. Morehouse et al., entitled"Architecture For Low Profile Rigid Disk Drive", which is incorporatedherein in its entirety.

Another object of the present invention is to provide a rigid disk drivewith increased packaging density and decreased height by placingelectronic circuitry in the interior free-volume of the disk drivehousing, not swept by elements of the actuator/transducer assembly.

A further object of the present invention is to reduce the powerconsumed by the rigid disk drive by operating the disk drive from asingle low voltage supply, such as 3.0 volts DC, rather than 5.0 voltsor 12 volts, as is customarily required, thereby allowing improvedefficiency when used as a battery powered device.

In accordance with another feature of the invention, a digitalelectronic signal interface is provided for the head disk assembly (HDA)whereby any analog disk drive signals, such as track position servo andread/write signals, are processed within the HDA and converted todigital form, thereby eliminating low level analog signals, minimizingeffects of electrical interference and providing an ideal connectionmeans when the disk drive is used as a circuit board component.

Another object of the present invention is to provide a removable diskdrive storage system which includes an improved shock mounting means asdisclosed in commonly assigned U.S. Pat. No. 5,149,048, issued Sep. 22,1992, by James H. Morehouse et al., entitled "Shock Absorbent MountingArrangement for Disk Drive or Other Component" which is incorporatedherein by reference in its entirety.

In accordance with another feature of the present invention, a diskdrive is provided which includes an improved disk clamp for retainingthe disks securely mounted to the spindle.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent froma study of the specification and drawings in which:

FIG. 1 is an exploded perspective view of a rigid disk drive inaccordance with the present invention;

FIG. 2A is a top-plan view of one embodiment of a rigid disk drive inaccordance with the present invention;

FIG. 2B is a view taken along the lines of 2B--2B in FIG. 2A;

FIG. 2C is a view taken along the lines of 2C--2C of FIG. 2A;

FIG. 2D is a top-plan view of an alternative embodiment of a rigid diskin accordance with the present invention which utilizes a resilientcover and a pluggable connector;

FIG. 2E is a view taken along the lines 2E--2E of FIG. 2D;

FIG. 2F is a view taken along the lines 2F--2F of FIG. 2D;

FIG. 3A is a top-plan view of a dynamic head loading version of a diskdrive in the course of the present invention;

FIG. 3B is a top-plan view of a contact start-stop version of a rigiddisk drive in accordance with the present invention;

FIG. 3C is a top-plan, highly enlarged view of the inner crash stop fora rigid disk drive in accordance with the present invention;

FIG. 4 is a cross-sectional view taken along the lines 4--4 of FIG. 3B;

FIG. 5A is an exploded perspective view of the rotary actuator portionof a version of the disk drive in accordance with the present inventionwhich utilizes dynamic loading and unloading and includes an inertiallatch;

FIG. 5B is an exploded, enlarged perspective view of the rotary actuatorportion of a rigid disk drive which utilizes the contact start/stop headtechnology;

FIG. 5C is a perspective view of cam assembly 18;

FIG. 6A is a plan view of a load beam utilized in the dynamichead-loading version of a disk drive in accordance with the presentinvention;

FIG. 6B is a view taken along lines 6B--6B in FIG. 6A;

FIG. 6C is a view taken along lines 6C--6C in FIG. 6A;

FIG. 6C-1 is a top plan view of a portion of a load beam used in thepresent invention;

FIG. 6C-2 is a cross sectional view taken along lines 6C-2-6C-2 in FIG.6C-1;

FIG. 6D is a cross-sectional view taken along lines 6D--6D in FIG. 6A;

FIG. 6E is a cross-sectional view taken along lines 6E--6E in FIG. 6A;

FIG. 6F is a cross-sectional view taken along lines 6F--6F in FIG. 6A;

FIG. 6G is a top-plan view of a load beam used in the dynamic head-loadversion of drive in accordance with the present invention;

FIG. 6H is a view taken along lines 6H--6H in FIG. 6G showing the loadbeam in the loaded position;

FIG. 6I illustrates the load beam in FIG. 6H, but in an unloadedposition;

FIG. 6J illustrates the flexure utilized to support the read/writemagnetic recording head on the load beam;

FIG. 6K illustrates in plan view of the underside of a load beam in thecontact start/stop version of the disk drive in accordance with thepresent invention;

FIG. 6L is a view taken along the line 6L--6L of FIG. 6K;

FIG. 7A is a combined electrical block diagram and partial structuraldiagram of one embodiment of a disk drive in accordance with the presentinvention;

FIG. 7B is a combined electrical block diagram and partial structuraldiagram of a disk drive in accordance with an alternative embodiment ofthe present invention;

FIG. 8 is a block diagram level circuit for the spin control anddrivers;

FIG. 9 is a circuit diagram of a spin motor drive circuit utilized withone version of the present invention;

FIG. 10 is a block diagram of the read/write circuitry utilized with thepresent invention;

FIG. 11 is a block diagram of the actuator driver and power-off unloadcircuit utilized with the present invention;

FIG. 12A is an illustration of a typical sector utilized on a magneticrecording disk of the head disk assembly in accordance with one versionof the present invention;

FIG. 12B is a timing diagram of the window signals produced by theprogrammable low-power timer circuit of the gate array illustrated inFIG. 13;

FIG. 12C is a timing diagram of the window signals produced by thedigital demodulator & Gray code address separator of the gate arraycircuit of FIG. 13;

FIG. 12D is a timing diagram of the window signals produced by thedigital demodulator & Gray code address separator of the gate arraycircuit of FIG. 13;

FIG. 13 is a block diagram of a gate array circuit which may be usedwith one embodiment of the present invention;

FIG. 14 is a block diagram of the A/D & D/A circuitry;

FIG. 15 illustrates in block-diagram form the gate array circuitutilized in conjunction with the alternative servo system, the servopattern of which is illustrated in FIG. 12D;

FIG. 16 illustrates a disk drive that includes a disk having theembedded servo system of this invention.

FIG. 17 is a linear representation of one embodiment of the embeddedservo field according to the principles of this invention.

FIG. 18 illustrates one embodiment of a magnetization pattern of theservo field according to the principles of this invention.

FIG. 19 illustrates one embodiment of a signal trace generated when thehead is positioned over the track centerline of the servo fieldaccording to the principles of this invention.

FIG. 20 is a timing diagram for signals used in conjunction with theservo field of this invention.

FIG. 21A to 21H are a scale drawing of the magnetization pattern for oneservo field of this invention that includes timing information for thevarious signals used to detect the servo information.

FIG. 22A to 22C illustrate the error immunity obtained insynchronization using the principles of this invention.

FIG. 23 is a cross-sectional view of one disk on which the prerecordedinterleaved embedded servo system of this invention is used.

FIG. 24A is a linear representation of a prior art servo field.

FIG. 24B illustrates a typical magnetization pattern for the prior artservo field of FIG. 1A.

FIG. 24C is the signal trace associated with the magnetization patternfor track 3 in Fig. 1B.

FIG. 25 is a block diagram of the adaptive runout compensation system ofthis invention that illustrates its relationship with the servocompensator of the disk drive.

FIG. 26 is a detailed block diagram of the secondary servo compensatorof this invention.

FIG. 27A is an example of a position error signal.

FIG. 27B illustrates the position error signal after the adaptive runoutcompensation method of this invention is used to process the signal ofFIG. 27A.

FIG. 28 is a flow diagram of the adaptive runout compensation method ofthis invention.

FIGS. 29A, 29B and 29C are top plan, bottom plan and side elevationalviews, respectively, of an embodiment of a clamp in accordance with theinvention.

FIG. 30 is a detailed view of the fingers, nubs and L-shaped legs inrelation to a disk and a hub, when the clamp is in an unstressedcondition.

FIGS. 31 and 32A and 32B are detailed views of the fingers, nubs andL-shaped legs in relation to a disk and a hub, when the clamp is in astressed condition.

FIG. 33 is a top view of the annular ring of the clamp in a stressed andunstressed condition.

FIG. 34 is an overall cross-sectional view showing how a disk is mountedwith the clamp of this invention.

FIG. 35 is a graph illustrating the behavior of a clamp according tothis invention when subjected to a shock force.

FIGS. 36, 37, 38, 39A, 39B, 39C, 40A, 40B, 40C, 41, 42A and 42Billustrate alternative embodiments according to this invention.

FIG. 43 is a section view of an HDA incorporating an architectureaccording to the present invention.

FIG. 44 is a plan view of the disk drive device of the presentinvention.

FIG. 45 is a section view of a two-disk HDA according to the presentinvention.

FIG. 46 is a simplified side view of a three-disk HDA according to thepresent invention.

FIGS. 47A-47H are simplified side views of a various prior art andpresent HDA embodiments.

FIGS. 48A and 48B are side views of alternative embodiments of thepresent invention incorporating two- and three-disk structures.

FIGS. 49A and 49B are side views of two- and three-disk embodiments ofHDAs incorporating a prior art low-profile motor architecture.

FIG. 50 illustrates a second embodiment of the invention.

FIG. 51A and 51B illustrate top and side elevational views,respectively, of the inertial body in the embodiment of FIG. 50.

FIG. 52 is an exploded view showing how the inertial latch of FIG. 50 ismounted on a disk drive.

FIGS. 53A and 53B are top and side elevational views of the sleeve inthe inertial latch of FIG. 50.

FIGS. 54A and 54B are top and side elevational views of the spring inthe inertial latch of FIG. 50.

FIG. 55 illustrates a third embodiment of the invention.

FIGS. 56A and 56B illustrate top and side elevational views,respectively, of the inertial latch of FIG. 55.

FIG. 57 is a detailed view showing how the inertial latch of FIG. 55 ismounted in a disk drive.

FIG. 58 is a detailed elevational view of the inertial latch of FIG. 55.

FIG. 59 illustrates the inertial latch of FIG. 55 in a locked position.

FIG. 60 illustrates the manner of mounting the inertial latch of FIG.55.

DETAILED DESCRIPTION OF THE INVENTION

Development and production of miniature laptop and hand held computersis constrained by available disk drives that are either too large,consume excessive battery power (limiting computer operating missiontime) or are not rugged enough to withstand the demanding shock andvibration requirements of portable operation. The disk drive describedin this invention, combining several unique features, provides asolution to the need for a miniature rigid disk drive informationstorage device with the performance and capacity previously availableonly in larger form factors. Present 2 1/2", 3 1/2" or even 1.8" formfactor disk drives do not provide the reduced power consumption or theshock and vibration durability of the disk drive described herein.

Microminiature hard disk drive 1 in accordance with one embodiment ofthe present invention is illustrated in FIGS. 1 and 2A-2C. A portion ofthe electronics for the rigid disk drive is included internally of thecase (or HDA) and a second portion of the electronics is included on theprinted circuit board 2, best illustrated in FIG. 1. Referring to FIG.2A, the approximate width of rigid disk drive 1 is 35 mm (measured fromperipheral edge 32 to peripheral edge 33) and the depth of rigid diskdrive 1 is approximately 50.8 mm (measured from peripheral edge 34 toperipheral edge 35). Thus, the footprint of rigid disk drive 1 is 35 mmby 50.8 mm. Various heights of the rigid disk drive may be utilized toconform to desired standards, such as, for example, 6.3 mm, 10 mm, 12.7mm, or 15 mm. Rigid disk drive 1 may be utilized in a stackedconfiguration with printed circuit board 2, this configuration beingillustrated in FIGS. 2A through 2C. In this stacked arrangement, thecombined depth from the top of rigid disk drive 1 to the bottom ofprinted circuit board 2 is approximately 10 mm. The head disk assemblyportion of rigid disk drive 1 weighs less than 50 grams, has a sealedconductive housing and cover, enclosing a single (as shown in FIG. 1) ormultiple rigid disks clamped to a combined spin motor and spindlebearing assembly. The spin motor uses flexible circuit interconnectmeans. Also enclosed in the housing is a rotary actuator mechanismcomprising a bearing assembly, magnetic read/write transducers mountedon load beams, a flexible circuit interconnect means, an actuator coiland permanent magnet structure. The disk drive has operating shocklimits of 10 G and non-operating shock limits of 200 G.

Table 1 below indicates the specifications for microminiature rigid diskdrive 1 in a version utilizing a single platter of magnetic media. Theinformation in parenthesis in the following table are for the translatemode (also known as the emulation mode) for the drive.

                  TABLE I                                                         ______________________________________                                        Capacity Per Drive         21.4 MegaBytes                                     Formatted                                                                              Per Track         (8704 Bytes)                                                Per Sector        512 Bytes                                                   Sectors Per Track (17)                                               Functional                                                                             Recording Density (BPI)                                                                         65,800                                                      Flux Density (FCI)                                                                              49,400                                                      Areal Density (MB/sq in)                                                                        179                                                         Disks             1                                                           Disk Diameter     33.5 mm                                                     Data Heads        2(4)                                                        Data Cylinders    (615)                                                       Track Density (TPI)                                                                             2775                                                        Recording Method  1,7 RLL Code                                       Performance                                                                            Media transfer Rate                                                                             1.61 to 2.56 MB/sec                                         Interface Transfer Rate                                                                         Up to 4.0 MB/sec                                            Rotational Speed  3,571 RPM                                                   Latency           8.5 ms                                                      Average Seek Time <20 ms                                                      Track to Track Seek Time                                                                        8 ms                                                        Maximum Seek time 30 ms                                                       Start Time (Typical)                                                                            1.5 sec                                                     Buffer Size       32 Kbytes                                                   Interface         AT/XT                                              Reliability                                                                            MTBF              100,000 hours                                               Start/Stops       1,000,000                                                   Unrecoverable Data                                                                              <1 per 10.sup.13                                            Error Rate        bits read                                          Power    +3 VDC + 5 V ± 5%                                                                            0.3 Amps                                                    Startup Current                                                               +5 VDC + 5 V ± 5%                                                                            0.5 Amps                                                    Startup Current                                                               Typical Heat Dissipation                                                      Spin-up           2.5 watts                                                   Idle              0.8 watts                                                   Read/Write/Seek   1.75 watts                                                  Power Savings Mode                                                                              0.4 watts                                                   Standby Mode      0.030 watts                                                 Sleep mode        0.010 watts                                        Environ- Temperature                                                          mental   Operating         +5° C. to +55° C.                             Nonoperating      -40° C. to +70° C.                            Relative Humidity 10% to 90% non-                                                               condensing                                                  Maximum Wet Bulb  30° C.                                               Shock (11 ms)                                                                 Operating         10 G                                                        Nonoperating      200 G                                                       Vibration (0 to peak)                                                         Operating         2 G                                                         Nonoperating      10 G                                                        Altitude                                                                      Operating         -1,000 to                                                                     10,000 feet                                                 Nonoperating (maximum)                                                                          40,000 feet                                        Physical Stacked Configuration                                                                           10 mm × 41 mm ×                                 (HDA & PCB)       50.8 mm                                                     Low Profile Configuration:                                                                      6.3 mm × 35 mm ×                                Head Disk Assembly                                                                              50.8 mm                                                     (HDA with one disk)                                                           Electronics Card (PCBA)                                                                         5 mm × 41 mm ×                                                    50.8 mm                                                     Weight            <50 grams                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Preliminary    Substrate                                                      Disk Specifications                                                                          Material     Aluminum                                                         OD           33.5 ± .025 mm                                                ID           10.00 ± .02 mm                                                             -00 mm                                                           Thickness    0.445 ± 0.02 mm                                               Concentricity                                                                              0.025 mm                                                         Clamp Zone                                                                    IR           5.3 mm                                                           OR           6.5 mm                                                           Glide Zone                                                                    IR           6.8 mm                                                           OR           15.7 mm                                                          Data Zone                                                                     IR           9.4 mm                                                           OR           15.5 mm                                                          Coercivity   1500 oe                                                          BRT          10,000 G- μin.                                                Glide Height 1.8 μin.                                       ______________________________________                                    

An inertial latch, which is described and claimed in commonly assignedU.S. Pat. No. 5,189,576, issued Aug. 21, 1992, by J. Morehouse entitled"Rotary Inertial Latch For Disk Drive Actuator" which is incorporatedherein by reference in its entirety, is used to prevent theactuator/head assembly from becoming dislodged while parked due to highin-plane shock and vibrational forces. This latch provides a lockingmechanism that does not increase actuator frictional forces or requireadditional power to maintain the actuator in the parked position.

Hard disk drive 1 operates with a single supply voltage of 3.0 volts or5.0 volts, with the following 3 volt power specifications:

Spin-up 2.5 watts

Idle 0.8 watts

Read/Write/Seek 1.75 watts

Power Saving Mode 0.4 watts

Standby Mode 0.030 watts

Sleep Mode 0.010 watts

Referring to FIG. 1, spin motor 3 is of a low power design, and isoptimized for low voltage operation. A major problem that must be solvedrelates to voltage head-room, which is defined as: V₋₋ headroom=(V₋₋supply-RPM×Ke) where Ke is in units of Volts/1000 RPM. In practice V₋₋supply is less than the power supply voltage because of intrinsic andirreducible switching transistor voltage losses and other parasiticvoltage drops, and required RPM is an independent variable, given byelements related to information transfer rates, access time andacceptable power dissipation considerations. Since the only availableelement design variable is Ke, motor optimization must concentrate onthis element. Disk drive 1 employs spin motor 3 that incorporates astator having two sets of windings. The first set is used in normalrunning and is optimized to have maximum operating efficiency with theavailable voltage overhead. The second set of windings is used for twopurposes, first to obtain sufficient starting torque with the limitedvoltage overhead, the second winding is operated in parallel with thefirst allowing the effective ampere-turns to be increased withoutincreasing Ke, allowing rapid spin up from power saving sleep mode. Inthe second configuration the first and second coils are connected inseries, to provide a back EMF generator during power down to unload themagnetic heads from the surface of the disk and latch the actuator inthe parked position. Spin motor 3 may take the form of the spin motordescribed and claimed in co-pending and commonly assigned U.S. patentapplication Ser. No. 07/630,110 of J. Morehouse et al. filed Dec. 19,1990, entitled "Spin Motor for a Hard Disk Assembly", which isincorporated herein by reference in its entirety. A spin motor controlsystem as illustrated and described in co-pending and commonly assignedU.S. patent application Ser. No. 07/630,470 of M. Utenick et al. filedDec. 19, 1990 entitled "Spin Motor Control System for a Hard DiskAssembly", which is also incorporated herein by reference in itsentirety is desirably used in conjunction with the above-described spinmotor. The complex motor switching task is incorporated in a uniquemotor commutating integrated circuit. Further motor optimization can beaccomplished by increasing the diameter of the rotors and stator whichallows reducing the motor thickness as well as achieving lower statorcoil resistance.

Close proximity of the spin motor to the read-write heads is inevitablebecause of the small dimensions of the disk drive. Switching noisegenerated by the commutating of the windings is a major source of highfrequency interference. When induced into the transducer heads, thisnoise results in servo and information errors by interfering withdemodulation of the servo and information read signals. This problem ispartially addressed by using ferrite shielding members, having highpermeability in the region of servo and read signal frequencies,employed on the transducer heads and at critical locations in the HDA.Other methods such as sine wave excitation, synchronous commutation andvariable slew rate excitation and synchronous servo demodulation withprecisely timed commutation also can be used to minimize the generationunwanted noise spikes.

Jitter, or rotational speed variation, is an important designconsideration caused by the reduced angular momentum of the miniaturizedrecording disk. To minimize cogging the number of motor phases can beincreased to greater than three or the number of poles can be increased,to 16 rather than 12 for example. Other methods for reducing jitterinclude closing the spin motor control loop with signals derived fromtrack following sampled sector servo data.

Methods which require increased servo sample rates are undesirable ifthey reduce the disk drive formatted capacity, significantly increasethe complexity of the sampling system or require the microprocessorcontroller to operate beyond its available bandwidth. This inventionemploys an innovative servo system, described in detail below, whichincreases the number of samples per second, providing improved errorimmunity without increasing the servo overhead.

Reducing spin motor power consumption is a complex problem. Threefactors affect motor power efficiency. First, the motor spindle bearingassembly must have very low non-repeatable run-out, this generallyrequires the use of a pre-loaded ball bearing cartridge. Friction inthis type of bearing is dependent on the amount of pre-load and the typeof non-migrating lubricant used. A second element of power consumptionis due to electrical losses in the motor. These losses can be minimizedby using of high energy, rare earth, magnets and a low loss magnet andpole structure along with low resistance stator windings. A third typeof power loss is due to windage losses caused by the spinning diskitself resulting in heat generation by the Joule effect. This source ofloss can be minimized by using a single disk of reduced diameter, suchas about 11/2 disk instead of a 2.5" disk, rotating at the lowestpractical speed.

Another method to reduce motor starting torque requirements is toimplement a method of dynamic loading and unloading the magnetictransducers from the surface of the rotating disk whereby friction dueto head disk contact, found in conventional contact start-stop diskdrives, is eliminated. A further advantage of this method is eliminationof head disk "stiction" that can occur when the heads cling to the disksurface stalling the spin motor or causing damage to the head diskinterface. Further, in order to minimize battery power in portablecomputing equipment, disk drives are subject to many more power-down andparking cycles are experienced than is typically expected in largersystems. Dynamic head loading and unloading provides increased longevityof the head/disk interface by allowing more than 1 million power downcycles without degradation due to friction and wear of the transducersand disk information surface, compared with 20 thousand cycles forconventional contact start-stop configurations. Rigid disk drive 1 mayutilize the dynamic head load/unload structure of the type described andclaimed in co-pending and commonly assigned U.S. patent application Ser.No. 07/629,957 of J. Morehouse et al. filed Dec. 19, 1990 entitled"Rigid Disk Drive With Dynamic Head Loading Apparatus", which isincorporated herein by reference in its entirety. An alternative dynamichead loading structure, which is fully described hereinafter in FIGS. 6Athrough 6I, may also be utilized in hard disk drive 1.

In an alternative embodiment of the present invention, microminiaturehard disk drive 4 (illustrated in top plan view in FIG. 3B) utilizes thecontact start/stop technique in which the heads are parked on a portionof the disk surface, which ideally is not used for information storage,and which also may be textured in order to minimize the clinging of theheads to the disk. Implementations of this type are known as contactstart/stop operation whereby the transducer heads land, take off and areparked on the disk surface as previously mentioned.

Rigid disk drives 1 (FIGS. 1 and 3A) and 4 (FIG. 3B) utilize embeddedservo and a track following sampled servo system designed to withstandincreased shock and vibration while making possible increasedinformation track densities, for example 3,000 tracks per inch, requiredto obtain the information storage capacity found in larger disk drives.Further, while more servo samples per second are required to improveservo performance, increased servo overhead cannot be allowed tosignificantly reduce usable storage capacity. As previously mentioned,an improved servo pre-recorded pattern and demodulation scheme isemployed that increases the number of servo fields and informationsectors from 48 to 72 per revolution without increasing the relativeoverhead. These and other improvements are possible by using uniquemulti-function servo field mapping used in an embedded servo system,which is described and claimed in portions of the servo pattern layoutillustrated herein in FIGS. 12D. The entire servo system is describedand claimed in the above-mentioned U.S. patent application Ser. No.07/765,348, which is co-pending and commonly assigned, which applicationis incorporated by reference in its entirety.

According to the principles of this invention, a novel embedded servosystem is used in a disk drive 1600 (FIG. 16). The interface of a diskdrive with a computer system and in particular the electronics requiredin conjunction with an embedded servo system to read and write data ondisks 1601 in response to signals from a disk controller to interfaceconnection 1615 are known to those skilled in the art.

As illustrated in FIG. 16, disk drive 1600 contains one or more circularplanar disks 1601. Each disk is coated on at least one side with amagnetic medium as on the prior art disk. Data are recorded byread/write head 1602 in concentric circular tracks on the disk, e.g.tracks 1621-i and 1621-(i+1). Corresponding tracks on different disksurfaces are approximately cylindrically aligned.

Each track is segmented into one or more sectors SCT-01, SCT-02, . . . ,SCT-n by prerecorded information in embedded servo field regions 1620-1through 1620-n. Each servo field region 1620-j where j=1, 2, . . . , n,includes m servo fields, where m is the number of concentric circulardata tracks on disk, i.e., one servo field in each data track atposition j for a total of nm servo fields per surface. In oneembodiment, as described more completely below, disks 1601 are 1.89inches (48 mm) in diameter and have 632 data tracks.

Unlike the prior art embedded servo systems where each data field had awrite-to-read transition region and each prerecorded servo field hadonly one AGC sub-field, the prerecorded embedded servo fields of thisinvention have substantially enhanced the amount of AGC data availablewithout either increasing the servo field overhead or decreasing theseek and track following performance of the disk drive. This isaccomplished by using various sub-fields within the servo field of thisinvention for two functions concurrently, as described more completelybelow.

Briefly, a first sub-field provides data for positioning the read/writehead and the first sub-field is simultaneously used as an AGC field fora second sub-field. Thus, the first sub-field performs two servofunctions simultaneously. Further, in one embodiment of the servo fieldof this invention, the cylinder address sub-field and the positionsub-field are no longer adjacent to one another in contrast to the priorart servo fields.

Servo field 1700, shown in FIG. 17, of this invention is a full trackaddress servo field. In a preferred embodiment, servo field 1700includes, in one embodiment, six sub-fields which are: 1) a firstautomatic gain control recovery sub-field 1700; 2) an index/AGCsub-field 1702; 3) a cylinder address/AGC sub-field 1703; 4) a sectormark sub-field 1704; 5) a second automatic gain control sub-field 1705;and 6) a position sub-field 1706.

A typical magnetization pattern 1800 for each of the sub-fields of servofield 1700 is illustrated in FIG. 18. In FIG. 18, the direction ofrotation of the disk is shown and four arbitrary tracks are shown andarbitrarily labeled as "cylinder 0" to "cylinder 3." The polarity of themagnetization pattern in FIG. 18 is illustrative only of one embodimentof the invention and is not intended to limit the polarity to thatshown. As is well-known to those skilled in the art, the magnetizationpattern works equally well in either polarity. A detailed expansion forone track of magnetization pattern 1800 is illustrated in FIGS. 21A to21H, which are drawn to scale and described more completely below.

FIG. 19 illustrates a typical waveform 1900 generated by magnetizationpattern 1800 for servo field 1700 when the read/write head is preciselyon the track centerline. Waveform 1900 is also explained more completelybelow. FIGS. 18 and 19 illustrate several important aspects of thisinvention. First, the magnetization pattern is continuous betweentracks. The continuity provides reliable AGC data during seeks when theread/write head is off a track centerline.

Second, all patterns that provide AGC data and position sub-field 1706have two time periods, i.e., time period T1 and time period T2, wheretime period T1 is defined as the time interval from a peak of a firstpolarity to a peak of a second polarity. Time period T2 is an integermultiple of time period T1. If two peaks occur in the first time period,e.g., the signal trace goes from a positive peak to a negative peak, thenegative peak is used to generate a clock pulse. Following a clockpulse, data is recorded in a second time period. The second time periodis T2. Thus, the combination of a clock pulse and a data bit is repeatedin the pattern with a period of period T1 plus period T2. In thisembodiment, clock pulses are negative pulses and data pulses arepositive pulses. The polarity of the clock and data pulses is arbitraryand either polarity will work so long as the clock pulses and the datapulses are of opposite polarity.

The trace of the data pulse within second period T2 determines whetherthe data represents a logic one or a logic zero. Specifically, thelocation of the positive peak within period T2 determines whether thedata is a one or a zero. If the positive peak occurs before threequarters of period T2, the data is a one. One data pulses are indicatedby the solid line waveform in sub-fields 1902 and 1903 in FIG. 19.Conversely, if the positive peak occurs at or after three quarters ofperiod T2, the data is a zero. Zero data pulses are indicated by thebroken line waveform in sub-fields 1902 and 1903 in FIG. 19.

In addition to the novel servo field of this invention, thewrite-to-read recovery field at the end of each data region is utilizedfor additional AGC data in all modes of operation except following awrite, as described more completely below. The use of the write-to-readrecovery field for AGC data aids in providing additional AGC marginwithout increasing the servo field overhead. While the prior art servofield 2400 included AGC data in the write-to-read recovery field, theAGC data was not utilized. Consequently, the prior art failed torecognize the advantages gained through the use of the write-to-readrecovery field for AGC.

AGC sub-field 1701 (FIG. 17) is in this embodiment four bits in lengthwhere one bit corresponds to the first time period T1. Hereinafter, areference to the length of a servo pattern sub-field in bits means atime period equal to time period T1. The "bit" used in defining thesub-field length should not be confused with a data bit. As explainedmore completely below, index/AGC sub-field 1702 and cylinder address/AGCsub-field 1703 provide both index and cylinder address informationconcurrently with AGC data. First AGC sub-field 1701 provides additionalAGC margin. In another embodiment, first AGC sub-field 1701 is notutilized and AGC depends solely on sub-fields 1702 and 1703. FIG. 19illustrates waveform 1901 generated by magnetic pattern 1801 in firstAGC sub-field 1701.

Index/AGC sub-field 1702 is 9 bits in length in this embodiment.Index/AGC sub-field 1702 contains three bits of data. Unlike prior artindex sub-fields that were used to identify only one sector in eachtrack, according to the principles of this invention, index/AGCsub-field 1702 is used to uniquely identify each sector in the track, asexplained more completely below.

When the index is lost, index/AGC sub-field 1702 is used to reestablishthe index as each subsequent index/AGC sub-field 1702 passes underread/write head 1602. Therefore, the index is typically establishedafter at most three sectors and usually only two sectors have passedunder read/write head 1602. If the track has 72 sectors, this means thatthe index is established on the average within about 1/32 of arevolution of the disk.

Prior art systems required waiting on the average for one-halfrevolution of the disk until the sector with the index mark passed underthe read/write head. Therefore, index/AGC sub-field 1702 enhances thecapture of the index reference and thereby reduces the rotationallatency, i.e., the time spent waiting to re-establish index, over theprior art index sub-field.

Further, index/AGC sub-field 1702 provides a uniquely identifiable fieldfor each track sector so that sub-field 1702 is used for a servo patternintegrity check during seeks, as explained more completely below.Waveform 1902 is an example of the signal generated by magnetic pattern1802 in index/AGC sub-field 1702.

Cylinder address/AGC sub-field 1703 includes a Gray code full trackaddress. In this embodiment, cylinder address/AGC sub-field is thirtybits in length. The use of Gray code track addresses is fundamentallythe same as in the prior art systems. However, as explained morecompletely below, the Grey code sequence is frequency modulated and thismodulation is an important aspect of this invention because the Graycode is used for AGC as well as for determining the track address.Waveform 1903 illustrates the possible signals generated by magneticpattern 1803 in cylinder address/AGC sub-field 1703.

Sector mark sub-field 1704 is 18 bits in length. As the name suggests,sector mark sub-field 1704 is used to precisely identify, i.e., mark,the circumferential location of each sector in the track. The firsteleven bits in sub-field 1704 are a fully DC erased gap. The importantaspect of the fully DC erased gap length is that the length is longerthan the longest gap in cylinder address/AGC sub-field 1703 when thelongest gap is bounded on either side by a single bit error.

The fully DC erased gap in sector mark sub-field 1704 is used to providea readily identifiable region for (i) initiation of synchronization and(ii) capturing the track address in the electronic circuitry. Therefore,failure to provide a DC erased gap of sufficient length introducesproblems whenever a single bit error occurs in cylinder address/AGCsub-field 1703 next to the longest gap in sub-field 1703. As illustratedin FIG. 19, the signal generated by this gap is a null signal.

Following the DC erased gap in sector mark sub-field 1704 is a firstsynchronization bit 1804A that generates a first synchronization pulse1904A. The first synchronization bit is followed by a second DC erasedregion of about five bits in length. A second synchronization bit 1804Bfollows the second DC erased region. The length of the second DC erasedregion is selected to allow sufficient time between the generation oftwo synchronization pulses 1904A and 1904B so that the two pulses can bedistinguished under the timing variations that may result either fromthe loss of a clock pulse or the loss of a data pulse in cylinderaddress sub-field 1703.

As explained more completely below, a novel detection method is used sothat if first synchronization (sync) pulse 1904A is missed, sync timingis obtained from second sync pulse 1904B. The ability to obtain synctiming from either pulse in sector mark sub-field 1704 enhances theperformance of this disk drive over disk drives with prior art embeddedservo systems that utilized a single sync pulse.

After sync timing is obtained, only position sub-field 1706 is needed tocomplete the servo operations. Reading of position sub-field 1706requires the most accuracy in AGC. As explained more completely below,the AGC level obtained from sub-fields 1702 and 1703 should be adequatefor precisely reading position sub-field 1706. Nevertheless, to assureprecision, second AGC sub-field 1705 is provided, which is twelve bitslong in this embodiment. Waveform 1905 is generated by magnetic pattern1805 in second AGC sub-field 1705.

Position sub-field 1706 is used to precisely center the read/write headon the track. Thus, cylinder address/AGC subfield 1703 is a courseindication of radial position of the read/write head and positionsub-field 1706 is a fine radial position indicator. In this embodiment,position sub-field 1706 includes an equal number of normal andquadrature frame pairs with the frame pairs interleaved. The peakamplitudes in position sub-field 1706 are sampled and held by the diskdrive electronics in a manner similar to prior art disk drives. The peakamplitudes are electronically averaged to obtain a radial positioningerror signal.

Herein, a normal frame refers to a frame that is recorded in half-trackpositions and a pair of normal frames include one frame with the regionabove the center line of the track recorded and another frame with theregion below the center line of the track recorded. A frame is anarbitrary unit of measure and is simply used to define the variousportions of position sub-field 1706 which is 39 bits in length. The twoframes in a normal pair of frames need not be directly adjacent to eachother. For example, a quadrature frame may be interposed between the twoframes that constitute the pair of normal frames. To assure that thedifference of the readback signals gives position information relativeto the track centerline, the normal frames change polarity in adjacenttracks.

A quadrature frame is a frame in which the information is recorded inthe on-track position and is either present or missing, in thisembodiment. A pair of quadrature frames include one frame with theon-track position magnetized and another frame with the on-trackposition unmagnetized. The two frames in a quadrature pair of frames arepreferably separated by a normal frame. Also, the quadrature framepolarity is opposite in adjacent tracks

FIG. 18 illustrates a magnetization pattern for one embodiment ofposition sub-field 1706 that consists of an equal number of normal andquadrature servo frame pairs. A first normal frame Na is followed by afirst quadrature frame Qa. Quadrature frame Qa is followed by a secondnormal frame Nb which in turn is followed by a second quadrature frameQb. The four frames Na, Qa, Nb, Qb form a cell that is repeated two moretimes to form a three cell position sub-field 1706 with a total oftwelve frames. The twelve frames include three pairs of normal framesN1, N2, N3, and three pairs of quadrature frames Q1, Q2, Q3. Each frameincludes either a pulse pair or no pulses.

The disk drive electronic circuitry inverts the negative pulses in thenormal frames Na and Nb and adds them together. The electronic circuitrysamples the height of the resulting positive peak from the normal framesand the height of the positive peak from the quadrature frames. Theaverage of the three peaks from the three cells is used to generate theposition error signal in a matter well known to those skilled in theart.

An important aspect of this invention is that the position data inposition sub-field 1706 contains frequencies common to the sub-fieldsused to obtain the AGC level. Specifically, pulse pairs are written withperiod T1 and are spaced apart from each other by at least period T2.The frequency content of position sub-field 1706 closely matches that ofthe AGC sub-fields and provides increased margin for the separation andproper detection of Quadrature and Normal position pulse information. Ifposition pulses are separated by at least period T2, the effects ofintersymbol interference are minimized.

Signal 2009 (FIG. 20) is timed from the sync pulse of the current sectorand is used to capture each Quadrature and Normal position pulse. Thewindow, i.e., the low portion of signal 2009, has a width of time T2 andthe time between windows is time T1. Position sub-field 1706 provideshighly accurate track following information.

Position sub-field 1706 is only illustrative of one embodiment of aposition sub-field suitable for use in the servo field of this inventionand is not intended to limit the invention to the particular embodimentdescribed. Other position sub-fields suitable for use in this inventionare described in the copending and commonly assigned U.S. patentapplication Ser. No. 07/630,475 entitled "Servo Field Scheme for HighSampling Rate and Reduced Overhead Embedded Servo Systems in DiskDrives," of John H. Blagaila et al. filed on Dec. 19, 1990, which isincorporated herein by reference.

A summary of the length for servo field 1700 of this invention is givenin Table 1.1. For comparison, the length of servo field 2400 is alsoestimated. The unit of measure chosen for comparison is a bit as definedabove, i.e., the period of time from a peak of one polarity to a peak ofa second polarity.

                  TABLE 1.1                                                       ______________________________________                                        Prior Art                                                                     Servo Field 2400                                                                              Servo Field 1700                                              Sub-field  Length   Sub-field       Length                                    ______________________________________                                        Write-to-Read                                                                            ˜27                                                                              Write-to-Read   37                                        AGC        ˜36                                                          Sector Mark                                                                              ˜21                                                                              AGC I            4                                        Index 1     ˜2                                                                              Index/AGC        9                                        Defect      ˜2                                                                              Cylinder Address/AGC                                                                          30                                        Cylinder Address                                                                         ˜25                                                                              Sector Mark     18                                        Index 2     ˜2                                                                              AGC II          12                                        Position   ˜28                                                                              Position        39                                        TOTAL      ˜143                                                                             TOTAL           149                                       % AGC (36/143)                                                                            25      % AGC(w write/read)                                                                           62                                                            (w/o write/read)                                                                              37                                        ______________________________________                                    

The ratio of the length of AGC data to the total servo field length issignificantly greater according to the principles of this invention eventhough the total servo field length is substantially the same as theprior art servo field. As explained above, the enhancement in the amountof AGC data is achieved by using several sub-fields for two servofunctions concurrently.

In this embodiment, the frequencies of the information in the servosub-fields used for AGC and another function concurrently are preferablyselected from within a bandwidth of frequencies that are common, or asnear to common as possible to every data region on the disk. For examplein one embodiment, the slowest data frequencies correspond to periods inthe range of 144 nanoseconds to 576 nanoseconds while the fastest datafrequencies correspond to periods in the range of 92 nanoseconds to 384nanoseconds. Thus, the two zones have a common range of 144 to 384nanoseconds. For this range, first time period T1 was selected as 208nanoseconds and second time period T2 was selected as 416 nanosecondsThis range of periods trades better resolution for slightly poorer AGCcontrol. Further, period T1 is common to the periods in both data zones.

As indicated above, index/AGC sub-field 1702 and cylinder address/AGCsub-field 1703 are used as AGC data for position sub-field 1706. Use ofcylinder address/AGC sub-field 1703 as both an AGC sub-field and acylinder address sub-field concurrently requires that the gaintransition from data region 1710 to cylinder address/AGC sub-field 1703is small so that only a small AGC adjustment is at most necessary forreading the cylinder address. Accordingly, the frequencies for the Graycode in cylinder address/AGC sub-field 1703 have been chosen so that thefrequencies are very similar to the frequencies of data region 1710,i.e., periods T1 and T2 are used in cylinder address/AGC sub-field 1707.Similarly, index/AGC sub-field 1702 is also written using these periodsso that the three data bits can be read and stored even though sub-field1702 occurs almost immediately at the start of servo field 1700.

Also as explained above, clock pulses have a first polarity, e.g.,negative, and data pulses have a second polarity that is different fromthe first polarity, e.g., positive. To read and save the index andcylinder address, the signal from read/write head 1602 is firstdemodulated.

Since the data is written in a frequency modulation format, as describedabove, any common frequency demodulation circuit may be used. Inaddition, the data on disk 1601 and consequently the data provided to orfrom read/write head 1602 is serial data. However, the data ispreferably supplied to disk drive microcontroller 1610 as parallel data.Consequently, the serial data signal from read/write head 1601 for servofield 1700 is deserialized with a shift register that contains two morebits than the number of data bits in cylinder address/AGC sub-field 1703and the index/AGC sub-field 1702.

The shift register is enabled prior to the start of index sub-field1702. The precise time that the shift register is enabled is notimportant so long as the shift register is enabled early enough to allowfor any timing variations so that no data bits of the index and cylinderdata are lost. In this embodiment, the signals from read/write head 1601are applied to the shift register at about 6,667 nanoseconds after thestart of write-to-read recovery area 1712. (See FIG. 21B).

The serial data signal from read/write head 1601 is first demodulated bythe frequency demodulator circuit. The output signal from the frequencydemodulator circuit is the input signal to the shift register.

Since index sub-field 1702 and cylinder address sub-field 1703 are bothwritten with frequency modulation that begins with a negative pulse andis followed by a positive data pulse, i.e., a pulse pair, the negativepulse is used as a clock bit so that servo pattern 1700 in thesesub-fields is self-synchronizing. Thus, the negative pulses (clockpulses) are used to initiate a clock signal that clocks the index andcylinder data through the shift register. This clock signal isresynchronized after every clock pulse generated by servo field 1700.The period of the clock signal is period T1 plus period T2.

Each data bit is clocked into the shift register and then seriallyshifted through the shift register. When a data bit reaches the end ofthe shift register, the data bit is shifted out of the register.Consequently, when DC erased gap is reached, the shift register containsthe track address and index.

Since index/AGC sub-field 1702 and cylinder address/AGC sub-field 1703are self-sychronizing, a data bit would normally be lost if either aclock bit or a data bit is dropped when reading these sub-fields. Inthis embodiment, when a data bit is missed, the subsequent clock bit isalso lost. However, the shift register clock signal is allowed to runfor one cycle without receiving a clock pulse from servo field 1700.Specifically, the previous clock pulse from servo field 1700 is used asa reference. However, if a second consecutive clock pulse from servofield 1700 is missed, the shift register clock signal is shut down.

The free running clock signal provides some timing robustness becausethe missed data bit had a fifty percent probability of being a zero.Thus, clocking a zero through the shift register in response to amissing data bit or clock bit in servo field 1700 results in eliminatingan error fifty percent of the time on the average.

When the DC erased gap begins, the shift register clock signal continuesfor two extra cycles and then stops. The shift register contains twoextra bits so that the last bits clocked in by the two extra clockcycles are ignored. The other bits in the shift register contain theindex and track address. After the DC erased gap is detected, the datais held in the shift register and the clock signal is disabled. Theindex and gray code read circuitry is turned off and the thirteen bitsfor the index and track address read from servo field 1700 are stored.

The three index bits represent a number between 0 and 7. The sequence ofindex numbers in the sectors is used as a course indicator of thecircumferential position of the read/write head. In this embodiment, thesequence of index numbers are the same for each track on the disk andare stored in firmware that is used by the disk drive microprocessor. Inone embodiment, the sequence is given in Table 2.1.

                  TABLE 2.1                                                       ______________________________________                                        Sec-                                                                          tor  Index   Sector  Index Sector                                                                              Index Sector                                                                              Index                            ______________________________________                                        0    0       18      2     36    2     54    4                                1    1       19      1     37    2     55    4                                2    0       20      3     38    5     56    5                                3    2       21      1     39    2     57    4                                4    2       22      4     40    2      8    4                                5    0       23      4     41    6     59    6                                6    3       24      1     42    2     60    4                                7    0       25      5     43    2     61    4                                8    4       26      1     44    7     62    7                                9    4       27      6     45    3     63    5                                10   0       28      1     46    4     64    6                                11   5       29      7     47    4     65    6                                12   0       30      2     48    3     66    5                                13   6       31      2     49    5     67    7                                14   0       32      3     50    3     68    7                                15   7       33      2     51    6     69    6                                16   1       34      2     52    3     70    6                                17   2       35      4     53    7     71    7                                ______________________________________                                    

After an index is stored in the shift register, the microprocessor savesthe index. After the microprocessor saves the index for the adjacentsector, the microprocessor can determine the circumferential position76% of the time from the two index numbers. Specifically, themicroprocessor compares the two index numbers with the data in Table 2.1to ascertain the sector number. However, if the two stored index numbersare the same, a third index number is required to identify the coarsecircumferential position of the read/write head. Thus, on the average2.24 sector reads are required to determine sector location. Hence,establishing index does not require waiting for one predetermined sectorto pass under the read/write head as in the prior art but rather, indexis always established within three sector reads.

In addition, index data provides an integrity check on the servo patternduring seeks in addition to those described more completely below.Herein, an "integrity check" means a check to establish that the servopattern is read correctly. If for some reason the servo timing is lostor perhaps a data bit is dropped, the servo pattern may be readincorrectly.

For example, during a seek read/write head 1601 may jump a variablenumber of tracks between servo sectors. Thus, the microprocessor onlyknows that the cylinder address should be within some range of tracks,but this is not sufficient for an accurate servo pattern integritycheck. In contrast, the index of this invention provides an integritycheck after reading at most three servo sectors.

Specifically, the microprocessor reads the index for two servo sectorsand uses Table 2.1 to project the index for the next servo sector if thetwo sector index values are different. If the two sector index valuesare the same, a third index value is read and Table 2.1 is then used toproject the index for the next servo sector. The microprocessor comparesthe projected index with the next index read. If the next index read andthe projected index are the same, the first integrity check of the servofield pattern has been verified. Using this process during seeks,enhances the seek performance of the disk drive by providing a warningof a potentially bad servo pattern. Thus, the index from index/AGCsub-field 1702 serves a dual function, i.e., coarse circumferentialpositioning and servo field integrity check. The use of sub-field 1702for these two functions plus the AGC function provides a significantamount of data without increasing the servo overhead.

In prior art systems, a dedicated set of bits were sometimes used as anintegrity check but these bits provided neither any information aboutindividual sectors nor AGC level. The dedicated set of integrity bitswas often times the only qualifier of a good servo field. Consequently,a single bit error in the prior art dedicated set of integrity bitscaused an increase in servo field sync loss or error rate.

According to the principles of this invention, the integrity check ofindex/AGC sub-field 1702 is only one of several integrity checks. Thus,if the index integrity check is bad, the additional servo zone integritychecks, described below, determine whether the servo information shouldbe used or only a part of it should be used. Another important point isthat the loss of any one integrity check does not result in the loss ofsync, whether it be the sector address (index), or cylinder address,sync1 missing, or sector window misalignment, that are described morecompletely below. A single bad integrity check only generates a warningthat the servo pattern is not pristine and should be treatedaccordingly.

For example, the write operation is the most dangerous mode of operationin the instance of an erroneous servo sector. Thus, in performing writesif any one of servo integrity checks fails typically the write operationshould stop immediately and report an error so that a reread of theservo field and a rewrite may be attempted. Conversely, in idle mode, ifany one of the integrity checks fail, no additional action is typicallytaken except perhaps some additional monitoring to see if the errorrepeats excessively in which case the sector may be flagged as a badsector.

Since the index/AGC and cylinder address AGC sub-fields 1702, 1703 areself-clocking and therefore do not require a synchronization (sync)pulse for timing, these sub-fields may be positioned before sector marksub-field 1704. As described above, sub-fields 1702, 1703 function asindex and cylinder address sub-fields as well as an AGC sub-field.However, additional AGC margin is provided by supplying first AGCsub-field 1701.

First AGC sub-field 1701 along with index mark sub-field 1702 andcylinder address sub-field 1703 is sufficient AGC data for accuratereading of both sector mark sub-field 1704 and position sub-field 1706.Note, as explained above, second AGC sub-field 1705 is provided, in oneembodiment, to provide additional AGC margin for position sub-field1706.

The index bits are only needed (i) in the early stages of the disk driveinitialization, (ii) for servo field integrity checks during seeks, or(iii) when the index is lost, i.e., the index bits are required onlywhen the index is being established or verified. In each of these cases,the disk drive is not in a write mode, and so write-to-read recoveryfield 1712 at the end of the data region 1710 is not needed forwrite-to-read recovery and thus can be used for AGC data for reading theindex bits. In write mode, sectors are counted to keep track of sectornumber and cylinder addresses are read so as to insure that data iswritten in the proper location.

Consequently, additional AGC data for index sub-field 1702 is providedin write-to-read recovery field 1712. To protect the bits residing inwrite-to-read recovery field 1712, a servo field write protect signal2001 goes active at about one microsecond after the start of thewrite-to-read recovery region and remains high until the next dataregion begins.

In FIG. 20, servo field write protect signal 2001, write mode AGC holdsignal 2002, AGC hold except for write mode signal 2003, sync1 sectorreference window 2006 and sync2 sector reference window 2008 are timed,typically using counters, from the synchronization pulse generated bysector mark sub-field 1704 in the previous servo sector field 1700. AGChold signals, after sync is established in the current sector, are timedfrom the current sector. Of course, this applies only to AGC sub-field1705, which is not used if sync is not established, i.e., the sector isnot found. Specifically, windows 2002A and 2003A are timed for sync inthe current sector so as to capture the AGC data in AGC sub-field 1705.

The time length of each of the servo sub-fields, the data region, andthe write-to-read recovery region are known. Accordingly, the delay timeafter the previous sector synchronization pulse until a particularsignal changes state is easily determined by simply counting the timethat has passed since the previous sector synchronization pulse.

Since the integrity of the write-to-read recovery field 1712 isprotected by servo zone write protect signal 2001, this field isavailable for AGC whenever the disk drive is not in write mode. Thereare at least three instances when the AGC data in write-to-read recoveryfield 1712 is used. These include (i) when the index bits are read toestablish the index; (ii) in pulse power mode, i.e., disabling the readchannel over the data regions, where the AGC value is lost between servofields; and (iii) in a seek, where there are no data under theread/write head.

Another important aspect of servo field 1700 of this invention is thatdata are ordered from the least correct AGC level needed to the mostcorrect AGC level needed to assure accurate reading of the servo data.Consequently, the servo pattern starts with bits that do not containdata, followed by index bits, which are read with the use of thewrite-to-read recovery field for AGC, the Gray code in cylinder addresssub-field 1703, sector mark sub-field 1704, and position sub-field 1706.This ordering of sub-fields assures that each sub-field is read with thenecessary AGC level to assure reliable operation.

Signals 2002 and 2003 (FIG. 20) indicate the AGC hold signal for thewrite mode and all other modes, respectively. While the AGC hold signalis active, e.g. high, the current AGC level is held. When the AGC holdsignal is inactive, e.g., low, the data being read is used to adjust theAGC level. Signals 2002 and 2003 show that sub-fields 1702, 1703 and1705 are used for AGC data as well as write-to-read recovery area 1712except in write mode. Time zero in FIG. 20 is about 188 microsecondsafter the first sync pulse in the previous servo field. The adjustmentof AGC level based upon AGC data is known to those skilled in the art

After obtaining a good AGC level from write-to-read recovery region 1712in all cases except following a write and from sub-fields 1701 to 1703,the disk drive read channel is prepared to detect the firstsynchronization (sync1) pulse 1904A and second synchronization (sync2)pulse 1904B generated by sector mark sub-field 1704.

If one of sync1 pulse 1904A and sync pulse 1904B is miscaptured, servoinformation following sector mark sub-field 1704 is either lost orcorrupt. It is important therefore to have immunity to errors indetecting the sync pulse and a method of detecting an incorrect syncpulse. Servo field 1700 of this invention has immunity to erroneous syncpulse generation or capture as well as a means for detecting anincorrect sync pulse.

With respect to error immunity, there are two types of servo field readerrors, missing bits and extra bits. Immunity to a single bit error isan important aspect of this invention. If the sync pattern in sectormark sub-field 1704 is susceptible to single bit errors, the syncpattern can be expected to be lost at the error rate inherent to thetechnology used. In disk drives this error rate is typically 1 in 10₁₀.

If it is possible to design a sync pattern, i.e., a sector marksub-field, that is only susceptible to errors of two or more bits thenthe immunity to errors increases dramatically. In disk drives, the errorrate for two independent errors is the square of the single bit errorrate. Using 1 in 10¹⁰ for the error rate of a single bit, a sync patternthat requires two independent bit errors results in an error rate of 1in 10²⁰ (since the errors are independent events their probabilitiesmultiply). Thus, if the sync pattern is immune to two independent biterrors, errors occur 10 billion times less frequently.

To obtain sync to the disk, an area prior to the actual sync bitlocation must be identified so that the hardware that triggers on thesync pulse can be set up. The area that is identified is the DC erasedgap in sector mark sub-field 1704. Specifically, the distance betweenpulses in servo field 1700 is monitored and when no pulses are detectedfor a predetermined period of time, typically about two microseconds inthis embodiment, hardware is enabled to detect the sync pulse.

Consequently, the DC erased gap must be neither falsely identified bythe occurrence of a missing bit in cylinder address sub-field 1703, normissed due to an extra pulse in the DC erased gap in sector marksub-field 1704. To permit Larger spin speed variations without losingthe sync timing, i.e., miscapturing the sync bit, the hardware thatdetects the DC gap is energized early in cylinder address/AGC sub-field1703.

Specifically, DC gap search window signal 2004 goes active at about 13microseconds after the start of write-to-read recovery region 1712. (Seealso FIG. 21D). DC gap search window 2004 remains active until about 19microseconds to account for spin speed variations. The DC erased gaplength must be chosen to be longer than any naturally occurring DCerased gap bounded by a single missing bit error, as described morecompletely below.

Since DC erased gap detection is started in cylinder address/AGCsub-field 1703 it is important that the qualification length for the DCerased gap is longer than any normally occurring DC erased gap withinthe Gray code track address. In addition for missing bit immunity, theDC erased gap must be longer than the longest normally occurring DCerased gap that can be produced in the Gray code by the occurrence ofone missing bit, i.e., longer than the longest normally occurring DCerased gap that can be produced by the occurrence of one missing bit inthe servo sub-field immediately preceding the DC erased gap.Consequently, the DC erased gap is in the range of 3*TDC to 36*TDC andis preferably about 10*TDC where time TDC is 166.667 nanoseconds in thisembodiment and is the length of the clock cycle used to increment the DCgap counter. Notice that period TDC is eight-tenths of period T1.

After the Gray code address is read, the DC erased gap must not becorrupted by an extra pulse that effectively hides the DC erased gap.The DC erased gap begins with the last negative pulse of the Gray codeaddress and ends a predetermined time following the absence of negativepulses. Positive pulses are ignored.

The read channel only permits positive pulses to follow negative pulsesand so if an error occurs, the read channel permits only a positiveerror pulse to propagate through after the last negative pulse of thecylinder address field. Since positive pulses are not detected whenmeasuring the DC gap, a positive error pulse has no effect. Thus, the DCgap is immune to single bit errors that generate a positive pulsefollowing the last negative pulse in cylinder sub-field 1703.

After the DC erased gap is detected, one of two sync pulses 1904A and1904B must be accurately detected. As explained above, the sync pulseidentifies the precise circumferential location of the sector on thetrack. If a spurious pulse is qualified as the sync pulse, subsequentservo, read, and writing timing signals are likely to be erroneous.Consequently, a part of the servo field may be overwritten by a writeoperation and this would ruin the disk drive until the disk embeddedservo pattern was reconstructed at the factory.

Thus, according to the principles of this invention, a novel method thatcompensates for (i) a single bit error in the magnetization pattern,(ii) spin motor speed variations and (iii) normal sampling variations isused to qualify the synchronization pulse. Briefly, firstsynchronization pulse 1904A must be located within a first window 2005Areferenced to the start of the DC erased gap, referred to as the sync1DC reference window, and a first window 2006A referenced to thesynchronization pulse for the immediately preceding sector, referred toas the sync1 sector reference window.

If first sync pulse 1904A is coincident with both windows 2005A, 2006A,first sync pulse 1904A is qualified and used. If the firstsynchronization pulse 1904A is coincident with window 2005A, but notwith window 2006A the first sync pulse 1904A is still qualified andused. However, an error is reported which implies a error in spin speedor a possible erroneous sync1 pulse.

If first sync pulse 1904A does not align with either window 2005A,2006A, it is ignored and synchronization may still be established withsecond synchronization pulse 1904B using substantially the same criteriafor windows 2007A and 2008A that was described above for sync1 pulse1904A with regard to windows 2005A and 2006A.

Synchronization may be achieved with either first or secondsynchronization pulses 1904A, 1904B. If first sync pulse 1904A isqualified, second sync pulse 1904B is ignored. To further explain thenovel synchronization method, the criteria for locating the variouswindows, the width of the windows, and the elimination of spurious ormissing pulses is described more completely below using FIGS. 21A to21H. Herein, a reference to a window being open refers to the width ofthe window.

In FIGS. 21A to 21H, similar features have the same base referencenumeral followed by a letter corresponding to the letter designating thefigure. Rows 2152A to 2152H are one continuous radial magnetizationpattern for a representative servo field 1700 of this invention. Servofield magnetization pattern 2152A to 2152H is broken into several piecesfor ease of presentation only. Rows 2151A to 2151H represent a period oftime equal to 333.3333 nanoseconds (8*41.66667) nanoseconds. Thus, theend of period 24 in row 2151B corresponds to about 8000 nanoseconds.Rows 2155E to 2158E and 2155F to 2158F represent clock interval TDC usedto increment the DC gap counter. In this embodiment, each clock intervalTDC is one-half the time period in row 2151. The reference numerals inthe six hundreds in FIGS. 21A to 21H represent the time of thecorresponding edge or feature in FIG. 20.

The use of a particular time in the Figures is illustrative only of oneembodiment of the invention. The important aspect is not the actual timevalues, but as explained more completely below, the relativerelationship of the various regions in the servo field and timing of thesignals used to capture the information in the servo field.

Leading edge 2005A-L of sync1 DC reference window 2005A is selectedassuming that the last bit in the Grey code cylinder address is properlyread. As illustrated in FIG. 21E, the DC gap counter is reset by thenegative pulse with a peak at the end of time period 49 in row 2151E.The DC gap counter is incremented by each of the clock tickscorresponding to the periods in row 2155E. When the DC gap counterreaches the count "11", as explained above, the DC erased gap isqualified and so hardware to generate sync1 DC reference window 2005A isenabled. On the next clock edge, i.e., the start of period 12 in row2155E, leading edge 605A-L is triggered. Hence, sync1 DC referencewindow 2005A starts immediately, i.e., opens, after the DC erased gap isqualified.

The width of sync1 DC reference window 2005A is selected to assureproper reading of the position data in position sub-field 1706 if sync1pulse 1904A falls within window 2005A, i.e., sync1 pulse 1904A occurswhile window 2005A is open. As explained above, each pulse pair inposition sub-field 1706 has a period of T1 and pulse pairs are spacedapart from each other by a period of T2, where periods T1 and T2 weredefined above and period T2 is twice period T1. Hence, in thisembodiment, if sync1 pulse 1904A falls within a window that is about3*T1 in width, the position pulses in sub-field 306 are still correctlydetected. Since period T1 is 208 nanoseconds, sync1 DC reference window2005A is preferably less than 624 nanoseconds in width. Thus, the widthof sync1 DC reference window 2005A was selected as 500 nanoseconds,i.e., three DC gap counter clock periods TDC wide, as shown in row2155E.

In addition to assuring proper detection of the position data, thiswidth window also compensates for normal variations in sampling thestart of the DC erased gap. There may be up to one clock pulse delay insampling the start of the DC erased gap in which case the DC gap counterwould be incremented as shown in row 2156E. In this case, sync1 DCreference window 2005A would start one DC gap clock cycle later, butwindow 2005A is still three clock periods TDC wide. Hence, as shown inFIG. 21E, first sync mark 1804A falls within the window that is enclosedin box 2005A.

Thus, the first requirement for qualification of first sync pulse 1904Ais that the pulse occur with a first predetermined time after a selectedreference point in the servo field, i.e., the start of the DC erasedgap. However, another qualification is also used to assure that propertiming is achieved.

The second qualification is derived from the previous synchronizationpulse. As indicated above, the distance between synchronization pulsesis a precise circumferential distance so that the time period betweensync pulses is known. Thus, a counter could simply be started and whenthe counter reached the time interval between synchronization pulses,circuitry is enabled to capture the next sync pulse. However, thisassumes that the spin speed of the disk is an unvarying constant. Infact, the spin speed varies about the specified speed "S" by an amount±V. Thus, to allow for spin speed variation, a window with a width W2 isselected where width W2 is given by:

    W2=(120/S)*(1/No. of sectors/track))*(V/100)

where

S is the spin motor speed in revolutions per minute

V is allowed variation in spin motor speed expressed in percent.

In this embodiment, speed S is 3571 rpm. The number of sectors per trackis seventy-two and speed variation V is ±0.2%. For these values, windowwidth W2 is calculated as 0.93 microseconds. Hence, the width of window2006A and 2008A was selected as one microsecond which is substantiallyequal to width W2. Window width W2 is centered about the point where thesynchronization pulse would be located if the spin motor speed was infact a constant, i.e., about 233 microseconds after the previoussynchronization pulse.

As illustrated in FIG. 21F, the negative sync1 pulse starts atsynchronization mark 1804A which is 56.25 time periods (row 2151F) afterthe start of write-to-read recovery region 1712. Therefore, first sync1sector reference window is centered about this point and so starts at55.75 time periods and ends 58.75 time periods after the start ofwrite-to-read recovery region 1712, where the time period is 333.33nanoseconds.

First sync1 pulse 1904A is not accepted unless it falls within sync1 DCgap reference window 2005A. An error is reported if it does not alsofall within sync1 sector reference window 2006A. For example, if anerror causes the DC erased gap to be prematurely detected, sync1 pulse1904A would still be within sync1 sector reference window 2006A, but notwithin sync1 DC gap reference window 2005A which would have occurred ata much earlier time. Consequently, sync is not established in this caseby sync1 pulse 1904A.

Even when sync is not established on sync1 pulse 1904A, sync may stillbe established with sync2 pulse 1904B. As explained above, to obtainsync from sync2 pulse 1904B, pulse 1904B must be coincident with sync2DC gap reference window 2007A. The location and width of sync2 sectorreference window 2008A are chosen in the same manner as described abovefor sync1 sector reference window except the window is centered aboutsecond sync mark 1804B which is about 233 microseconds after the secondsync mark in the previous sector.

The leading edge and width of sync2 DC gap reference window 2007A areselected by considering the reasons why first sync pulse 1904A may bemissed. If the last bit in the Gray code cylinder address is dropped ormissing, the DC gap counter is started as shown in row 2157E, or in row2158E with a sampling error. Consequently, sync1 DC gap reference window2005A occurs to early. To capture sync2 pulse 1904B, the tolerances onsync2 DC gap reference window 2007A are greatly relaxed.

In this embodiment, window 2007A is started so that when the last Greycode bit is lost, window 2007A overlaps with the sync1 DC gap referencewindow 2005A when a sampling error occurs in determining the start ofthe DC erased gap as illustrated in rows 2156F and 2157F. Thus, asillustrated in FIG. 21F, the leading edge of the window is at 18.5*TDCwhich in this embodiment is about 3,083 nanoseconds after the start ofthe DC erased gap. In one embodiment, the DC gap counter is used togenerate a signal at 18*TDC that in turn generates window 2007A.

The width of window 2007A is selected so that sync2 DC gap referencewindow 2007A extends at least one clock period TDC after the peak ofsync2 pulse 1904B when the last bit in the Grey code cylinder address islost. Thus, as shown in FIG. 21F, the window extends from 18.5*TDCseconds to 25.5*TDC after the start of the DC erased gap when the lastbit in the Gray code cylinder address is dropped or missing as shown inrow 2157E. Thus, sync2 DC gap reference window 2007A is 7*TDC secondswide, e.g., about 1,167 nanoseconds.

Row 2155F illustrates the location of sync2 DC gap reference window2007A when the start of the DC erased gap is detected normally. Row2156F illustrates the location of sync2 DC gap reference window 2007Awhen the start of the DC erased gap is detected following a samplingerror and row 2158F illustrates the location of sync2 DC gap referencewindow when the start of the DC erased gap is detected following asampling error and when the last bit in the Gray code cylinder addressis dropped or missing. In each of these cases, sync2 pulse 1904B fallswithin sync2 DC gap reference window 2007A.

When sync2 pulse 1904B falls within sync2 sector reference window 2008Aand sync2 DC gap reference window 2007, sync is established. However,since a error must occur to not sync on sync1 pulse 1904A, an error isflagged and the write mode of operation is inhibited in one embodimentIf sync is obtained on sync1 pulse 1904A in the next sector, operationcontinues normally. However after a predetermined number of consecutivesyncs on sync2 pulse 1904B, typically three or four, a problem clearlyexists and the disk drive must be resynchronized.

In prior art systems, if sync was lost on the sync1 pulse,resynchronization was necessary. However, the use of the novel methoddescribed above maintains sync even when sync on sync1 pulse 1904A islost. Consequently, this method enhances operation of the disk driveover prior art systems. Specifically, FIGS. 22A to 22C illustrate inmore detail the robustness of sync operation using the method of thisinvention.

In FIG. 22A, sync1 pulse 1904A is missing. However, sync2 pulse 1904B iscoincident with sycn2 DC gap reference window 2007A and sync2 sectorreference window 2008A. Thus, sync is obtained with sync2 pulse 1904B.When sync is obtained from sync2 pulse 1904B, processing is transferredto a point in hardware so as to compensate for the time differencebetween sync1 pulse 1904A and sync2 pulse 1904B.

In FIG. 22B, the last bit in the Gray code cylinder address is missingand so the DC erased gap is qualified prematurely. Consequently, sync1DC gap reference window 2005A occurs early and coincidence is notobtained between sync1 pulse 1904A and the two windows 2005A and 2006A.However, sync is maintained by capture of sync2 pulse 1904B.

FIG. 22C illustrates an extraneous positive pulse which has no affect onthe windows. Consequently, sync is obtained from sync1 pulse 1904A.

Another qualification of the sync timing is a measure of the accuracywith which the index and cylinder addresses are read sector to sector.If the index or gray code data bits are determined incorrect, the syncis suspect and appropriate action taken, e.g., a flag is set to indicatethat if errors persist in subsequent sectors reading the index and graycode data bits, corrective action is required.

The use of the two windows in synchronization provides an easy means toprovide further power reduction for a disk drive and maintainsynchronization. Specifically, either the counter used for the sync DCgap reference window or the counter used for the sync sector referencewindow may be programmed to count for two sectors rather than one sothat sync is established only for every other sector. This would permitthe read channel to remain inactive over the servo field for the skippedover sector and thereby reduce power consumption. The extension toskipping 2, 3, 4, or even an arbitrary number of sectors follows thesame principle and requires only an appropriate adjustment of thecounters used. Hence, only a subset of the servo fields in a track areread thereby reducing power consumption when the disk drive is idle.

FIG. 23 is a cross-sectional view of a disk on which the prerecordedembedded servo system of this invention is used in one embodiment. Interradius IR of the disk data is about 13.4 mm and outer radius OR of thedata area is about 22.1 mm. Hence, the data area DA of the diskincluding guard bands at the inner and outer radii is about 8.7 mm. Thedisk has a density of about 40,000 bpi and 1550 tracks per inch. Thedisk is mounted on a hub with a radius HR of about 6 mm. Inner crashstop ICS is at about a radius of 12.7 mm and is nominally touched at aradius ICS of about 13.1 mm. Loading/unloading ramp 1603 (FIG. 16) isnominally touched at a radius TNR of about 22.7 mm. Alternatively, theservo system described and claimed in co-pending and commonly assignedU.S. patent application Ser. No. 07/630,475 of J. Blagaila et al. filedDec. 19, 1990 entitled "Servo Field Scheme For High Sampling Rate",which is also incorporated herein by reference in its entirety, may beutilized in practicing the present invention.

Another problem with track following servo systems employed in highdensity disk drives is what is known as settling time, defined as thetime after arrival on track when the transducer head position iscentered on the track. Common practice has been to use a fixed timer todelay the onset of writing until a time greater than the worst casesettling time has elapsed. Since many track seeking operations use shortseeks resulting in rapid servo settling time, unnecessary delays canoccur when reading or writing information. This problem is particularlysevere when the disk drive is subjected to severe shock while reading orwriting information resulting in unacceptably slow recovery time. Thisproblem is addressed by incorporation of an adaptive method whereby theservo system determines, by way of preset limit conditions, if thetransducer is on-track and settled within acceptable limits. Furtheradvantages of this method are that the position servo stiffness, whichis determined by the servo gain and bandwidth, can be reduced in orderto avoid excitation of mechanical resonances that occur in conventionalsystems. Other adaptive means to improve track following withoutrequiring increased servo bandwidth and sample rate are run-out andthermal compensation by microprocessor control.

Disk drives that employ an embedded sampled servo system cannot read orrespond to track position information while writing contiguous sectorsof information without significant overhead. The present inventionincorporates staggered servo patterns, a dual read channel, andprovisions for a head on another disk surface to read and supply data tothe track following servo system. This method results in improved trackfollowing accuracy, noise immunity and spin motor velocity control.

According to the principles of this invention a novel disk runoutcompensation system, which is described more completely below, is usedin a miniature disk drive 1600 (FIG. 16). Disk drive 1600 contains oneor more circular planar disks 1601. Each disk is coated on at least oneside with a magnetic medium as in the prior art disk. Data are recordedby read/write head 1602 in concentric circular tracks on the disk, e.g.tracks 1621-i and 1621-(i+1). Corresponding tracks on different disksurfaces are approximately cylindrically aligned.

Each track is segmented into one or more sectors SCT-01, SCT-02, . . . ,SCT-n by prerecorded information in embedded servo field regions 1620-1through 1620-n. Each servo field region 1620-j where j=1, 2, . . . , n,includes m servo fields, where m is the number of concentric circulardata tracks on disk, i.e., one servo field in each data track atposition j for a total of nm servo fields per surface. In oneembodiment, as described more completely below, disks 1601 are 1.89inches (48 mm) in diameter and have 632 data tracks.

The interface of disk drive 1600 with a computer system and theelectronics required in conjunction with an embedded servo system toread and write data on disk 1601 in response to signals from a diskcontroller to interface connection 1615 are known to those skilled inthe art. The radial and circumferential positioning of read/write head1602 using embedded servo data and a servo system is also well known. Inthis particular system, the servo system includes R/W preamp 1605,combined read/write circuit 1606, actuator A/D and D/A circuit 1612,actuator driver circuit 1613, gate array 1611, and microcontroller 1610.

In addition, microcontroller 1610 has access to memory 1650 for storingand retrieving data. Upon power-up of disk drive 1600, firmware for aproportional integral difference (PID) servo compensator, seek control,and a secondary servo compensator of this invention in ROM 1609 isloaded into microcontroller 1610. In this embodiment microcontroller1610 is a 46100 (HPC+) microprocessor supplied by National Semiconductorof Santa Clara, Calif.

The servo compensator in microcontroller 1610 receives a digitalposition error signal for a sector in the track and determines theposition correction needed to position read/write head 1602 over thecenterline of the track for that sector. The position correction is usedto generate a servo compensation signal for that sector. The servocompensator applies a gain factor to the servo compensation signal tocreate a digital actuator position adjustment signal for that sector.

Microcontroller 1610 sends the digital actuator position adjustmentsignal to a D/A converter that resides in actuator A/D and D/A circuit1612. The actuator position adjustment signal is processed and appliedto the actuator in a conventional fashion. This process is sequentiallyrepeated for each sector in a track.

Disk 1601 is clamped to the disk drive as described in copending,commonly assigned and concurrently filed herewith, U.S. patentapplication Ser. No. 07/765,358, entitled "Clamp for Information StorageDisk," of James Dunckley, which is incorporated herein by reference inits entirety. The disk clamp does not apply sufficient pressure on disk1601 to hold it rigidly in place about the center of rotation 1630 ofdisk drive 1600. Therefore, if disk drive 1600 is subjected to vibrationor shock, disk 1601 is likely to be radially displaced and the center ofthe disk will be displaced from true center of rotation 1630. Asexplained above, the servo system can not reliably position read/writehead 1602 in these circumstances.

Thus, according to the principles of this invention, a secondary servocompensator 2500 (FIG. 25) is provided in microcontroller 1610.Secondary servo compensator 2500 functions independently of servocompensator 2510 and provides on-line real-time compensation for diskrunout that occurs during operation of disk drive 1600. Specifically,servo compensator 2510 receives position error signal 1699 and generatesactuator position adjustment signal 2511, as described above.Simultaneously, secondary servo compensator 2500 receives position errorsignal 1699, and as described more completely below, analyzes the diskrunout and simultaneously generates a runout compensation signal 2501during operation of disk drive 1600, i.e., while disk drive 1600 isidle, reading, or writing.

Actuator signal generator 2520 combines actuator adjustment signal 2511that is generated using position error signal 1699 from sector "i" andrunout compensation signal 2501 that is generated using position errorsignal 1699 for sector "i-1" to create a runout compensated actuatorsignal 2521 for sector "i". Here "i" is a sector number. Hence, therunout compensation is fed forward when microcontroller 1610 providesrunout compensated actuator adjustment signal 2521 to the servo system.The servo system, using the information from servo compensator 2510 andsecondary servo compensator 2500, continuously maintains read/write head1602 over the desired track centerline independent of the offset of thecenter of disk 1601 from true center of rotation 1630.

Unlike prior art systems, that required multiple revolutions to generatea runout correction and was useful only upon start-up of the disk drivebefore a read or a write was performed, secondary servo compensator 2500continuously monitors the position of disk 1601 relative to true centerof rotation 1630 and generates runout compensation signal 2501 whiledisk 1601 is being used. Since runout compensation signal 2501 isgenerated during operation of miniature disk drive 1600, the adaptiverunout compensation is transparent to the user.

Index and sector processor 2530 provides secondary servo compensator2500 sector number 2531 over which read/write head 1602 is positionedand a revolution number 2532. One embodiment for encoding the index andsector data in the embedded servo field for uniquely identifying eachsector and rapidly establishing index is disclosed in copending,commonly assigned, and concurrently filed herewith U.S. patentapplication Ser. NO. 07/765,348 entitled "An Embedded Servo System ForLow Power Disk Drives" of Stephen Cowen, which is incorporated herein byreference in its entirety.

FIG. 26 is a more detailed block diagram of secondary servo compensator2500. Secondary servo compensator 2500 includes a runout analyzer 2610and a runout compensation generator 2620 that each receive sector number2531 and revolution number 2532 from index and sector processor 2530.Runout analyzer 2610 sequentially receives digital position error signal1699 for each sector in a track, i.e., for each sector in a revolutionof disk 1601. Position error signal 1699 contains many harmonic andnon-repetitive components for disturbances other than runout, such aswindage, bearing noise and servo settling transients. For example, FIG.27A illustrates a typical position error signal 1699. Runout analyzer2610 filters position error signal 1699 to obtain the fundamental runoutfrequency sector by sector.

The filtering process in runout analyzer 2610 preferably starts with theindex sector and proceeds for each sector in a track. The filteringprocess separates the sector runout component from the position errorsignal during the sector period. The sector runout component for eachsector in a predetermined number of analysis revolutions n of disk 1601are accumulated in memory 2550, i.e., each sector runout component isadded to the sum of sector runout components stored in memory 2550.

After all the sectors in the predetermined number of analysisrevolutions n are processed, runout analyzer 2610 produces an averagedvalue of the sector runout components accumulated in memory 2550. Theaveraged value is a runout factor that is also stored in memory 2550. Asexplained more completely below, during the predetermined number ofanalysis revolutions n, runout compensation generator 2620 iscontinuously generating, sector by sector, runout compensation signal2501.

As the next revolution of disk 1601 starts after the predeterminednumber of analysis revolutions n, the sector runout components fromrunout analyzer 2610 are not accumulated in memory 2510 and are simplyignored. As runout compensation generator 2620 receives the sectornumber for each sector in the next revolution of disk 1601, generator2620 uses the runout factor stored in memory 2550 to generate a sectorrunout correction signal 2621 for that sector.

Sector runout correction signal 2621 is provided to gain adjustmentmeans 2630. In one embodiment, gain adjustment means 2630 multiplies thesector runout correction signal 2621 by the same gain factor that isused in servo compensator 2510 to generate runout compensation signal2501. However, the gain factor used in gain adjustment means 2630 may beequal or less than the gain factor in servo compensator 2510. In someservo systems, the gain factor used in gain adjustment means 2630 isless than the gain factor used in servo compensator 2510 to maintainstability of the servo system.

Since runout analyzer 2610 and runout compensation generator 2620require about one sector period to produce the runout compensation,runout compensation signal 2501 is fed forward to the next sector.Hence, runout compensation signal 2501 for sector "i-1" is combined withactuator position adjustment signal 2511 for sector "i" by actuatorsignal generator 2520 as described above, where sector "i" is adjacentto and follows sector "i-1" in a revolution.

The output from runout analyzer 2610 is not used in this revolution topermit settling of the servo system. While a single settling revolutionis described herein, the important factor is to provide sufficientrevolutions for the servo system to settle before further adjusting therunout compensation.

After the servo settling revolution, runout analyzer 2610 and runoutcompensator generator 2620 are both utilized on the next revolution ofdisk 1601 to maintain read/write head 1602 properly positioned. Runoutcompensation generator 2620 continues to generate sector by sectorrunout compensation signal 2501 as just described, i.e., using therunout factor from the prior runout analysis that is stored in memory2550. Simultaneously, runout analyzer 2610 produces a new runout factorfor the predetermined number of analysis revolutions n. Thus, secondaryservo compensator 2500 is updating the runout error data at the sametime as it is compensating for runout.

After all the sectors in the predetermined number of analysisrevolutions n are processed, a new runout factor is produced for the nrevolutions. The new runout factor is added to the runout factor storedin memory 2550 and the accumulated runout factor is then stored inmemory 2550, i.e., the runout factor is updated. Thus, runout analyzer2610 includes a means for accumulating the runout factor duringoperation of disk drive 1600.

After the runout factor is updated, the output from runout analyzer 2610is ignored during the next revolution of disk 1601 and runoutcompensator generator 2620 operates using the accumulated runout factorin memory 2550. This sequence of (i) generating a runout compensationsignal and simultaneously analyzing the runout sector by sector for apredetermined number of revolutions, and (ii) generating a runoutcompensation signal for a single revolution to allow the servo system tosettle is repeated continuously.

Thus, memory 2550 contains a runout factor that is a summation over timeof averaged sector by sector runout components. As is known to thoseskilled in the art, such a summation tends to smooth the response of asystem and ameliorate problems associated with short transients. Also,the accumulation of runout factors over time prevents discontinuitiesand assures that read/write head 1602 is maintained over the trackcenterline. Secondary servo compensator 2500 provides a reliablecontinuous on-line real time runout compensation signal so that data isnot overwritten as a consequence of disk slippage that occurs duringoperation. Hence, secondary servo compensator 2500 provides adaptiverunout compensation for miniature disk drives.

A more detailed description of one embodiment of the adaptive runoutcompensation system of this invention is given below. This embodiment isillustrative only of a preferred embodiment of the invention and is notintended to limit the invention to the particular embodiment described.

In this embodiment, the filtering process used in runout analyzer 2610is a discrete Fourier transform. As is known to those skilled in theart, the Fourier transform decomposes periodic waves forms into sine andcosine components. Here, only one frequency, disk runout, is ofinterest. The discrete Fourier transform separates the disk runout fromthe position error signal and gives a cosine runout component and a sinerunout component, i.e., the runout component has two parts in thisembodiment.

To create a period for the sine and cosine functions used in thediscrete Fourier transform, one revolution of disk 1601 is taken as theperiod. Thus, the sine and cosine functions are evaluated for eachsector in the track where the sectors are numbered from zero to (m-1)and where in this embodiment m is 72.

The discrete Fourier transform generates two runout transform terms,sometimes referred to as runout components. The first runout componentis given by: ##EQU1## where S=sector number being analyzed where S=0, 1,. . . , ((Tot. Sectors)-1);

Tot. Sectors=total number of sectors per disk revolution; and

PES=the position error signal

Similarly, the second runout component is given by: ##EQU2## whereS=number of sector being analyzed where S=0, 1, . . . , ((Tot.Sectors)-1);

Tot. Sectors=total number of sectors per disk revolution; and

PES=the position error signal.

In this embodiment, second runout components "CosineRunouts" and firstrunout components "SineRunouts" are each accumulated in memory 2550 forthe predetermined number of analysis revolutions n. Secondary servocompensator 2500 runs in real time and so the runout must be analyzedand runout compensation generated within a sector period. Hence, tospeed operation of secondary servo compensator 2500, the cosine term insecond runout component "CosineRunout_(s) " and the sine term in firstrunout component "SineRunout_(s) " are not repeatedly calculated.Rather, a table of the cosine terms for each sector and a table of thesine terms for each sector are accessed in ROM 1609. Of course,microcontroller 1610 could be used to generate the sine and cosine termsonce upon power-up of the disk driven and the resulting tables could bestored in memory 2550.

The representational values used in one embodiment of the sine table andthe cosine table are given in Tables 1.2 and 2.2 respectively. Thevalues given are in decimal. These numbers are mapped to byte values,i.e., seven data bits plus a sign bit.

                  TABLE 1.2                                                       ______________________________________                                        SINE TERM TABLE                                                               Sec-                                                                          tor  Sine    Sector  Sine  Sector                                                                              Sine  Sector                                                                              Sine                             No.  Term    No.     Term  No.   Term  No.   Term                             ______________________________________                                        0      0     18      -127  36     0    54    127                              1    -11     19      -127  37    11    55    127                              2    -22     20      -125  38    22    56    125                              3    -33     21      -123  39    33    57    123                              4    -43     22      -119  40    43    58    119                              5    -54     23      -115  41    54    59    115                              6    -64     24      -110  42    64    60    110                              7    -73     25      -104  43    73    61    104                              8    -82     26      -97   44    82    62    97                               9    -90     27      -90   45    90    63    90                               10   -97     28      -82   46    97    64    82                               11   -104    29      -73   47    104   65    73                               12   -110    30      -63   48    110   66    63                               13   -115    31      -54   49    115   67    54                               14   -119    32      -43   50    119   68    43                               15   -123    33      -33   51    123   69    33                               16   -125    34      -22   52    125   70    22                               17   -127    35      -11   53    127   71    11                               ______________________________________                                    

                  TABLE 2.2                                                       ______________________________________                                        COSINE TERM TABLE                                                             Sec-                                                                          tor  Cosine  Sector  Cosine                                                                              Sector                                                                              Cosine                                                                              Sector                                                                              Cosine                           No.  Term    No.     Term  No.   Term  No.   Term                             ______________________________________                                        0    127     18      -11   36    -127  54    11                               1    125     19      -22   37    -125  55    22                               2    123     20      -33   38    -123  56    33                               3    119     21      -43   39    -119  57    43                               4    115     22      -54   40    -115  58    54                               5    110     23      -64   41    -110  59    64                               6    104     24      -73   42    -104  60    73                               7    97      25      -82   43    -97   61    82                               8    90      26      -90   44    -90   62    90                               9    82      27      -97   45    -82   63    97                               10   73      28      -104  46    -73   64    104                              11   63      29      -110  47    -63   65    110                              12   54      30      -115  48    -54   66    115                              13   43      31      -119  49    -43   67    119                              14   33      32      -123  50    -33   68    123                              15   22      33      -125  51    -22   69    125                              16   11      34      -127  52    -11   70    127                              17    0      35      -127  53      0   71    127                              ______________________________________                                    

Prior to considering the use of the discrete Fourier transform in runoutanalyzer 2610, the predetermined number of revolutions n used by runoutanalyzer 2610 must be defined. The minimum number of predeterminedrevolutions is one. However, to obtain better sampling, a larger numberof revolutions is preferred. The maximum number of revolutions islimited by the word length used to store the accumulated runout factorin memory 2550 and the maximum radial displacement of disk 1601.

If the accumulated runout factor overflows for the maximum displacement,the runout compensation becomes meaningless. In this embodiment, theword length is 16 bits and considering the maximum radial displacementof disk 1601, four revolutions were selected as the predetermined numberof analysis revolutions.

The first step in adaptive compensation method 2800 of this invention isanalyze runout and simultaneously generate runout compensation 2801(FIG. 2B). Upon power-up of disk drive 1600, memory locations secondaryservo compensator 2500 are zeroed When the disk reaches a valid spinspeed secondary servo compensator 2500 is started.

Runout compensation generator 2620 generates a null signal for runoutcompensation during the first predetermined number of analysisrevolutions n after a valid spin speed is reached. As explained above,runout compensation generator 2620 uses the runout factor stored inmemory 2550 to generate runout correction signal 2621. Since initiallythe stored runout factor is zero, sector runout correction signal 2621for each sector in a revolution is also zero, and consequently runoutcompensation signal 2501

For each sector for the predetermined number of analysis revolutions n,runout analyzer 2610 retrieves the sine term from the sine table (TABLE1.2 above) in ROM 1609 for sector number 2531 received from index andsector processor 2530. Runout analyzer 2610 multiplies the sine term byposition error signal 1699 for sector number 2531 to obtain first runoutcomponent "SineRunout_(s) " for that sector. First sector runoutcomponents "SineRunout_(s) " are accumulated in location 2551 in memory2550. Specifically, each sector runout component "SineRunout_(s) " isadded to the accumulated sum of first sector runout components stored inlocation 2551 and the new accumulated sum is saved in location 2551.

Similarly, for each sector for the predetermined number of analysisrevolutions n, runout analyzer 2610 retrieves the cosine term from thecosine table (TABLE 2.2 above) in ROM 1609 for sector number 2531received from index and sector processor and multiplies the cosine termby position error signal to obtain second sector runout component"CosineRunout_(s) ". The second sector runout components are accumulatedin memory at location 2552.

Thus, the value at location 2551 in memory 2550 after the n analysisrevolutions is: ##EQU3## where S=sector number being analyzed where S=0,1, . . . , (m-1);

m=total number of sectors per disk revolution;

F=revolution number being analyzed where F=0,

1, . . . , (n-1); and

n=predetermined number of analysis revolutions.

and the value at location 2552 in memory 2550 after the n analysisrevolutions is: ##EQU4## where S=sector number being analyzed where S=0,1, . . . , (m-1);

m=total number of sectors per disk revolution;

F=revolution number being analyzed where F=0,

1, . . . , (n-1); and

n=predetermined number of analysis revolutions.

Recall that runout analyzer 2610 produces a runout factor using theaccumulated sector runout component stored in memory 2550. Since theaccumulated sector runout component is separated into accumulated sinerunout components and accumulated cosine runout components in thisembodiment, the runout factor is also separated into a sine runoutfactor and a cosine runout factor. Hence, after each sector in thepredetermined number of analysis revolutions n has been processed,runout analyzer 2610 forms a sine runout factor, "SineFactor", that isan averaged value of the accumulated sine runout components.Specifically, the sine runout factor is: ##EQU5## where n=predeterminednumber of analysis revolutions; and

m=total number of sectors per disk revolution;

The cosine runout factor, i.e., the averaged value of the cosine runoutcomponents, is: ##EQU6## where n=predetermined number of analysisrevolutions

m=total number of sectors per disk revolution;

The sine runout factor and the cosine runout factor are stored in memory2550 at locations 2553 and 2554, respectively. As explained above, inthis embodiment, locations 2553 and 2554 are each 16 bits in length.This completes step 2801 of adaptive runout compensation method 2800 ofthis invention.

In generate runout compensation step 2802 of adaptive runoutcompensation method 2800, which begins on the next revolution of disk1601 following the predetermined number of analysis revolutions n instep 2801, the two runout components from runout analyser 2610 for eachsector are not accumulated in memory 2550. For each sector, as indicatedby sector number 2531, runout compensation generator 2620 firstretrieves the appropriate sine term from the sine table (TABLE 1.2above) in ROM 1609 for the sector number and then multiplies the sineterm by the sine runout factor retrieved from memory location 2553 toform an inverse sine transform term.

Similarly, runout compensation generator 2620 retrieves the appropriatecosine term from the cosine table (TABLE 2.2 above) in ROM 1609 for thesector number and multiplies the cosine term by the cosine runout factorretrieved from memory location 2554 to form an inverse cosine transformterm. The inverse cosine transform term and the inverse sine transformterm are summed by runout compensation generator 2620 to generate sectorrunout correction signal 2621 for that sector. Specifically,:

    Sine Compensation.sub.s =SineFactor·(Sine Term).sub.s(7)

where

(Sine Term)_(s) =value in Table 1.2 for sector S; and

Cosine Compensation_(s) =CosineFactor·(Cosine Term)_(s)

where

(Cosine Term)_(s) =value in Table 2.2 for sector S.

    Runout Correction Signal.sub.s =Sine Compensation.sub.s +Cosine Compensation.sub.s                                        (9)

Gain adjustment means 2630 multiplies sector runout correction signal2621 by the gain factor, as described above, to generate runoutcompensation signal 2501. In this embodiment, actuator signal generator2520 sums runout compensation signal 2501 for sector "i-1" with actuatoradjustment signal 2511 for sector "i" to generate runout compensatedactuator signal 2521 for sector "i", as explained above.

Also, as described above, the generation of actuator position adjustmentsignal 2511 is well-known to those skilled in the art. Similarly,conversion of digital runout compensated actuator adjustment signal 2521to an analog signal and use of the analog signal to position read/writehead 1602 are well-known because the process is identical to the processthat was previously used for the uncompensated actuator positionadjustment signal.

After each sector in the track is processed in generate runoutcompensation step 2802 of adaptive runout compensation method 2800,processing returns to analyze runout and generate runout compensationstep 2801. In this step, the runout analysis and runout generation areagain simultaneously performed.

For each of the predetermined number of analysis revolutions n in thisstep, runout compensator 2620 uses the runout factors at locations 2553and 2554 respectively to generate runout compensation signal 2501 foreach sector. Similarly, the accumulation of sine runout components andcosine runout components for the n analysis revolutions is started over.After each sector in the predetermined number of analysis revolutions nhas been processed, runout analyzer 2610 forms a new sine runout factor"SineFactor" using the new accumulated sine runout components inlocation 2551 for the n analysis revolutions and a new cosine runoutfactor "CosineFactor" using the new accumulated cosine runout componentsin location 2552 for the n analysis revolutions.

The new sine runout factor is added to the sine runout factor"SineFactor" in location 2553 and the new cosine runout factor is addedto the cosine runout factor "CosineFactor" in location 2554 by runoutanalyzer 2601. Thus, the two runout factors are accumulated over timewhile disk drive 1600 is operating. This completes step 2801 andprocessing transfers to step 2802.

FIG. 27B illustrates the position error signal after the position errorsignal of FIG. 27A is processed by adaptive runout compensation method2800 of this invention. Notice that the large harmonic oscillations areeliminated so that read/write head 1602 is following the trackcenterline even though the center of disk 1601 is displaced from thecenter of rotation 1630.

The sampling provided by analyzing the runout for a predetermined numberof revolutions reduces the effects of spurious noise and enhances therunout correlation. Similarly, the accumulation of the runout factorsover time provides stability and assures that the runout compensationaccurately follows the disk runout. If track position is lost due to ashock or any other reason, secondary servo compensator 2500 is disableduntil track position is reestablished.

Rigid disk drives 1 and 4 utilize miniature read/write transducers 5,known as 50% heads, which have mean dimensions approximately one-halfthose of the previously known thin-film heads. Read/write transducers 5may be ferrite monolithic or composite type devices employing variouswriting and reading gap structures such as metal-in-gap (MIG). Othertypes of heads such as thin-film ring or magneto-resistive types may beemployed. Advantages of 50% sliders are decreased foot print, allowingmore information tracks to be placed on a disk, lower susceptibility toEMI, and less than one-eighth the mass of conventional sized headsproportionately reducing displacement forces when accelerations due toexternal shocks and impacts are encountered. In order to maintain highrecording density from inner to outer tracks, heads with nearly constantflying height are used, employing modified air-bearing designs such asTPC, cross slot designs and negative pressure methods, allowing mappingof additional information sectors at outer radii to achieve increasedareal storage efficiency. Read/write transducers 5 are illustrated inFIGS. 1, 5A, 5B, 6H, 6I, 6K and 6B.

Improvements in VLSI semiconductor technology, combined with otherbenefits derived from using a disk having a diameter of about 33.5 mm(11/4 inches), have reduced component count and power requirements. Thishas made it possible for servo, read/write and spin motor controlelectronics to be incorporated within the housing of rigid disk drives 1and 4 as part of the internal disk drive assembly flexible circuitinterconnect. Using TAB or COB (Chip On circuit Board) techniquesautomated assembly methods and higher circuit densities are practical atreduced cost. Increasing the number of electronic components in the diskdrive assembly housing reduces the number of external components,resulting in greater effective volumetric packaging density, reducedspin motor noise pickup, shielding of critical analog circuits frominterference from external noise sources, and reduction in the requirednumber of external interconnects. This feature is described in detail inconjunction with FIG. 7B. An important object of this feature is toeliminate external analog signals by digital signal processing withinthe disk drive enclosure, thereby providing for an all digital interfacebetween the components within the disk drive enclosure and the diskdrive components which are external of the disk drive housing.

The computer system interface to disk drives 1 and 4 may be any of anumber of industry standard types such as low power SCSI or AT Bus. Oneimplementation of the digital disk drive assembly interface such asillustrated in FIG. 7b allows direct circuit board interconnection tothe host computer, providing smaller disk drive package volume, fewerelectrical interconnections, and reduced power consumption by theelimination of complex bus interface. System physical interconnect meansfor such a small disk drive have become a major problem as the size ofavailable connectors approaches that of the disk drive. One solution isto use flexible circuit connection means, where the terminating end iseither soldered directly to the host or to a zero insertion force flexcircuit connector.

As disk drives have been reduced in size their physical mounting hasbecome a problem. Present methods require special mounting hardware,such as the miniature screws employed in making watches, which areimpractical to use in mass produced electronic assemblies. Thisinvention anticipates methods such as clam-shell or trapped mountingthereby entirely eliminating the need for conventional mounting means.This invention also incorporates features described and claimed incommonly assigned U.S. Pat. No. 5,161,770 of J. Morehouse et al. issuedNov. 10, 1992, entitled "Shock Absorbent Mounting Arrangement For DiskDrive or Other Component", which is incorporated herein reference in itsentirety.

Referring to FIG. 1, microminiature hard disk drive 1 is illustrated inexploded perspective in view, along with printed circuit board 2 whichis positioned beneath hard disk drive 1. Rigid disk drive 1 includesbaseplate 6 which may be comprised of cast aluminum material. Baseplate6 is a solid unitary structure which it includes an opening 7 which is,after assembly, closed by the mounting of spin motor 3, the peripheraledge of which extends slightly beyond the edge of opening 7. In additionto opening 7, an opening 8 is provided to permit air flow between theinterior of the enclosure and the exterior. A suitable air filter 9,having an external diameter larger than the internal diameter of opening8 is sealed to baseplate 6 to filter the air which enters the enclosureto prevent contaminating the interior of the disk drive. A substantiallyflat magnetic disk 10 is supported on spindle 11 for rotation. Magneticdisk 10 is suitably attached to spindle 11 to the use of a disk clamp12. Although various forms of clamping mechanisms may be utilized tosecurely attach magnetic disk 10 to spindle 11 of spin motor 3, aparticularly advantageous disk clamp is described and claimed incopending and commonly assigned U.S. patent application Ser. No.07/765,358 of James Dunckley, filed Sep. 25, 1991, entitled "Clamp forData Storage Disk", which is incorporated herein by reference in itsentirety. Spin motor 3 may take the form of, for example, the spin motorwhich is described and claimed in copending and commonly assigned U.S.patent application Ser. No. 07/630,110, filed Dec. 19, 1990, furtherdetails of which are described above.

FIGS. 29A, 29B and 29C are top plan, bottom plan and side elevationalviews of a clamp 10-4 in accordance with the invention. Clamp 10-4includes a basic annular ring 11-4 around which are integrally formedfingers 12-4, nubs 13-4 and L-shaped legs 14-4. As can be seen from FIG.29C, fingers 12-4 extend in the same direction from annular ring 11-4and are inclined slightly outwardly. The shape of nubs 13-4 and L-shapedlegs 14-4 can best be seen from FIGS. 30 and 31.

In this preferred embodiment clamp 10-4 is made of a plastic materialwhich is deformed or stressed slightly when it is placed in use. FIGS.30 and 31 show clamp 10-4 in an unstressed and stressed condition,respectively. FIGS. 30 and 31 are composite views which show nubs 13-1and L-shaped legs 14-1 taken through cross section I--I, shown in FIG.29A, and fingers 12-4 taken through cross section II--II, shown in FIG.29A. The cross section of unstressed annular ring 11-4 is shown in FIG.30, and the cross sections of stressed annular ring 11-4 are shown as11a and 11b in FIG. 31. 11a represents the position of annular ring 11-4at cross section I--I in FIG. 29A; 11b represents the position ofannular ring 11-4 at cross section II--II in FIG. 29A.

As can be seen from FIGS. 30 and 31, nub 13-4 makes contact with aninclined (conical) surface 15-4 of a hub 17-4 which tends to force nub13-4 (and L-shaped leg 14-4) downward and outward (to the left in FIGS.30 and 31). That is, the force vector F imposed on nub 13-4 isessentially normal to inclined surface 15-4, as shown by the arrow inFIG. 31. The vertical component F_(v) of the force vector F causesL-shaped leg 14-4 to apply an axial force F_(v) against a disk 16-4,thereby forcing it against a flat portion 18-4 of hub 17-4. Thehorizontal component F_(h) of the force vector F causes annular ring11-4 to be deformed outwardly, as reflected by cross section 11a.

FIGS. 32A and 32B are similar to FIG. 31, but show separate views takenat cross sections I--I and II--II, respectively, of FIG. 29A.

The deflection of annular ring 11-4 as a result of the horizontal forcecomponent F_(h) is illustrated (in a somewhat exaggerated fashion) inFIG. 33. The unstressed shape of annular ring 11-4 is shown in hatchedlines. The stressed shape of annular ring 11-4 is shown in solid lines.The positions of nubs 13-4 have been pushed radially outward while themidpoints 50-4 between nubs 13-4 have been drawn radially inward. Itwill be noted that the positions of the fingers 12-4 are approximatelythe same in the stressed and unstressed conditions.

Referring again to FIGS. 30 and 31, it is apparent that in the stressedcondition finger 12-4 applies an outward radial force against an edge19-4 of disk 16-4. This outward radial force, which is critical inclamping disk 16-4, is the sum total of three components: (i) thebending or deflection of annular ring 15-4 in the horizontal plane,represented by the distance d in FIG. 31; (ii) the twisting or torsionof annular ring 15-4, represented by the angle θ in FIG. 31; and (iii)the bending or flexure of finger 12-4. In the embodiment shown,components (i) and (ii) are of greater significance than component(iii).

The magnitude of components (i) and (ii) is a function of stiffness ofthe material of which annular ring 11-4 is made as well as the size andshape of the cross section of annular ring 11-4. The magnitude ofcomponent (iii) is a function of the same factors with respect tofingers 12-4.

An overall cross-sectional view showing the manner in which disk 16-4 isclamped to hub 17-4 is shown in FIG. 34. Included are a central shaft60-4 which rotates by means of bearings 61-4 within a stationary base62-4. Hub 17-4 is driven by a wound stator 63-4.

The arithmetic sum of the radial forces applied by fingers 12-4 (i.e.,the sum of the absolute magnitude of those forces) is substantiallygreater than the sum of the downward (axial) forces applied to disk 16-4by L-shaped legs 14-4. The axial forces are just sufficient to seat disk16-4 against the flat portion 18-4 of hub 17-4 and not enough to causewarpage in disk 16-4. The radial forces provided by fingers 12-4 arestrong enough to produce a static frictional force tangential to edge19-4 at the location of each finger 12-4 so as to prevent disk 16-4 fromslipping when it is accelerated or decelerated in a rotationaldirection.

The behavior of disk 16-4 in the presence of an inertial shock force canbe approximated by reference to the graph shown in FIG. 35, thehorizontal axis of which represents the horizontal displacement of disk16-4 from center (the origin), and the vertical axis which representsthe horizontal component of a shock force imposed on disk 16-4.

For purposes of this analysis, it is assumed that essentially two typesof forces are imposed on disk 16-4 as a result of its interaction withclamp 10-4 and hub 17-4: (i) a dynamic force F_(d), which increaseslinearly with the displacement of disk 16-4 from the origin, and (ii) astatic frictional force F_(f), which results from the contact of disk16-4 with clamp 10-4 and hub 17-4. The dynamic force F_(d) can berepresented as: where k is the stiffness of clamp 10-4 and x is thehorizontal displacement of disk 16-4. k is a function of the stiffnessof the material of which clamp 10-4 is made and represents the combinedeffect of the three elements described above, namely, the bending ordeflection of annular ring 15-4, the twisting or torsion of annular ring15-4, and the bending or flexure of fingers 12-4.

The frictional force F_(r) is approximated by the following formula:

    F.sub.f =3F.sub.n μ.sub.cd +3F.sub.n μ.sub.hd +2F.sub.finger μ.sub.cd                                               (2)

where F_(f) is the total frictional force on disk 16-4, F_(n) is thenormal force imposed on disk 16-4 by each of L-shaped legs 14-4,F_(finger) is the radial force imposed on disk 16-4 by each of fingers12-4, and μ_(cd) and μ_(hd) are the coefficients of friction between theclamp and disk and the hub and disk, respectively. The formula thus sumsthe frictional forces at each of the points of contact between disk 16-4and L-shaped legs 14-4, flat portions 18-4, and fingers 12-4. It isassumed that two fingers 12-4 are displaced 90° from the direction ofthe shock force and a frictional force arises from the contact of thesefingers 12-4 and inside edge 19-4 of disk 16-4.

Referring again to FIG. 35, when the disk is centered it is held inplace by the frictional force F_(f). It will remain centered unless theshock force imposed on it exceeds F_(f). This region is represented bythe line from the origin to point 1-4 in FIG. 35.

If the shock force exceeds F_(f), the disk will be displaced until thesum of F_(f) and the dynamic force F_(d) imposed by clamp 10-4 matchesthe magnitude of the shock force as represented by point 2-4. Point 2-4is not an equilibrium point, however, because the frictional force whichopposed the displacement of disk 16-4 disappears as soon as disk 16-4comes to a halt. This is represented by point 3-4, which also takes intoaccount that disk 16-4 experiences an outward frictional force as soonas it begins to return to the origin. Disk 16-4 thus returns to point4-4, where the frictional force is equal to the dynamic force imposed byclamp 10-4. At point 4-4,

    F.sub.f =F.sub.d =kx

thus, the abscissa x₄ of point 4-4 is equal to

    x.sub.4 =F.sub.f /k

If disk 16-4 is subjected to a shock force in the opposite direction, itwill pass through points 5-4, 6-4 and 7-4 in the same manner and end upat point 8-4. It should be noted that points 4-4 and 8-4 are worstcases; shock forces often occur in groups and may result in the diskcoming to rest somewhere on the x axis between points 4-4 and 8-4.

In designing clamp 10-4, it is desirable to minimize the finaldisplacement of disk 16-4 (F_(f) /k). This can be accomplished either byincreasing the stiffness k or reducing the normal force F_(n) on disk16-4, which determines the frictional force F_(f). Reducing thefrictional force F_(f) is not desirable, however, because this forceprovides the initial "stickiness" which prevents disk 16-4 from beingdisplaced at all when it is subjected to minimal shock forces (i.e.,shock forces located along the line from the origin to point 1-4 in FIG.35). The alternative is to increase the stiffness of clamp 10-4. Thiscan be accomplished by: (i) making clamp 10-4 from a material with ahigher Young's modulus, (ii) increasing the thickness of annular ring15-4, or (iii) reducing the preload dimensions of clamp 10-4. Theproblem with making clamp 10-4 from a material with a higher Young'smodulus (e.g., a metal or reinforced plastic material) is that thesematerials may not be able to withstand the distortion required toinstall disk 16-4 on clamp 10-4. Increasing the thickness of annularring 15 may also result in problems resulting from installationdistortion.

As an example, assume that the normal force F_(n) imposed by each ofL-shaped legs 14-4 is 49.6 gmf, the radial force F_(finger) imposed byeach of fingers 12-4 is 174 gmf, and μ_(cd) and μ_(hd) are each 0.3.Equation (2) yields an F_(f) equal to 193.7 gmf. If the mass of disk16-4 is 3 gm, the external "G" shock necessary to shift disk 16-4 is:193.7 gmf/3 gm=64.6 G. This is substantially above typical operatingshock specifications which are in the range of 10-20 G.

A clamp 10-4 made of polycarbonate has a k of 4108 gmf/mm. Applyingequation (1), this yields equilibrium displacement x₄ =193.7 gmf/4108gmf/mm=0.047 mm=0.001856 in. If the data are written at 2000 tracks perinch, this represents a displacement of 3.7 tracks. This error is withinthe range that can be corrected by once-around servo compensationschemes such as the one disclosed in U.S. patent application Ser. No.07/766,478, entitled "Adaptive Runout Compensation System for MiniatureDisk Drive", by Thomas L. Andrews, Jr., co-owned, commonly assigned, andfiled concurrently herewith.

Temperature variations are another possible cause of eccentricities indisk drives. The hubs are normally manufactured of steel and the disksare manufactured of aluminum, which have different coefficients ofthermal expansion. Using axial clamping, it is virtually impossible torestrain all relative motion between the disk and hub as the temperaturechanges. What normally happens is that the clamp has a maximum clampingforce at one point on the disk. This point becomes a "sticking point"and the disk and hub will slide with respect to one another in an areaopposite the sticking point, thereby producing an eccentricity. Everytemperature change has the potential of producing another unpredictableand non-repeatable eccentricity.

With the clamp of the this invention, the principal clamping force isradial, and the disk and hub are free to move relative to each otherwhile the clamp maintains them in a concentric relationship. Thus,temperature changes should not produce eccentricities like thosegenerated in axial clamping schemes.

In this embodiment, clamp 10-4 is manufactured of polycarbonate, butother plastics and spring-like materials are also suitable for thispurpose. One such material is a liquid crystal polymer known as Vectra™manufactured by Hoechst-Celanese Corporation of Chatham, N.J. The mostimportant characteristic of the material is that it be spring-like,i.e., that it have a linear stress-to-strain curve.

While the embodiment described above includes three nubs 13-4 andL-shaped legs 14-4 and six fingers 12-4, these numbers are not critical.Other clamps according to this invention may include a fewer or greaternumber of nubs, L-shaped legs and fingers. Similarly, while nubs 13-4are lined up with L-shaped legs 14-4 in this embodiment, this need notbe the case.

FIGS. 36, 37, 38, 39A, 39B, 39C, 40A, 40B, 40C, 41, 42A and 42Billustrate a number of alternative embodiments in accordance with theinvention. FIG. 36 shows a two-disk arrangement in which two clamps 80-4are used to mount disks 81-4 and 82-4, respectively. Clamps 80-4 aresubstantially similar to clamp 10-4. An annular flange 82-4 slips overhub 83-4 and rests on a circular step 84-4 formed in hub 83-4.

FIG. 37 illustrates an alternative two-disk arrangement in which theupper clamp 91-4 is inverted. Again, clamps 90-4 and 91-4 aresubstantially similar to clamp 10-4. A circular flange 92-4 is screwedconcentrically to the top of hub 93-4 and has an annular surface 94-4against which disk 81-4 is pressed by clamp 91-4.

FIG. 38 illustrates a two-disk arrangement in which a secondary hub100-4 is screwed onto a primary hub 101-4. Clamps 102-4 and 103-4 aresubstantially similar to clamp 10-4.

FIGS. 39A, 39B and 39C illustrate a substantially different radial clamp110-4 which has three upwardly projecting fingers 111-4 and threedownwardly projecting fingers 112-4. On the inside circumference ofannular ring 113-4, three contact surfaces 114-4 are located andopposite them, projecting outwardly, are three locating surfaces 115-4.Radial clamp 110-4 does not include elements comparable to the nubs 13-4or L-shaped legs 14-4 of clamp 10-4.

Clamp 110-4 is press-fitted over a hub 116-4, with the actual contactbeing at contact surfaces 114-4. Upper disk 81-4 is held in positionradially by fingers 111-4 and lower disk 82-4 is held in position byfingers 112-4. A solid annular spacer 117-4 fits around radial clamp110-4, coming into contact with locating surfaces 115-4, and separatesdisks 81-4 and 82-4. An upper flange 118-4 is screwed into hub 116-4 andtightened sufficiently to provide a proper axial force (approximately0.5 pounds) against disks 81-4 and 82-4. This axial force is transmittedfrom disk 81-4 to disk 82-4 by means of spacer 117-4. Spacer 117-4 andupper flange 118-4 can be made of plastic or metal. If desired, radialclamp 110-4 can be split into two annular pieces, one piece carryingupwardly projecting fingers 111-4 and the other piece carryingdownwardly projecting fingers 112-4. This may allow the addition of moreradial fingers and simplify the design of the mold for manufacturing theclamps.

The embodiment of FIG. 40A, 40B, and 4C are similar to that of FIG. 39A,39B, and 39C, except that solid spacer 117-4 has been replaced by anaxial spring 120-4. Axial spring 120-4, which is pictured in FIGS. 40Band 40C, is made of a plastic material and contains three upwardprojections 121-4 and three downward projections 122-4. Axial spring120-4 is sized such that when flange 118-4 is tightened a proper axialforce is imposed on disks 81-4 and 82-4 by projections 121-4 and 122-4,respectively. Clamp 110-4 imposes only a radial force on disks 81-4 and82-4.

FIG. 41 shows another embodiment of a two-disk arrangement. Upper clamp130-4 is similar to clamp 10-4. Lower clamp 131-4 is also similar toclamp 10-4, except that a projection 132-4 extends upward from each ofL-shaped legs 133-4. Upper disk 81-4 is supported by projections 132-4.Fingers 134-4 on clamps 130-4 and 131-4 are substantially similar tofingers 12-4 on clamp 10-4.

FIG. 42A and 42B illustrate a two-disk arrangement in which disks 81-4and 82-4 are separated by a spacer 140-4. Clamp 141-4 has nubs 142-4 andL-shaped legs 143-4, which are similar to those in clamp 10-4 andprovide an axial force against disk 81-4 and (via spacer 140-4) againstdisk 82-4. Clamp 141-4 contains two sets of fingers. Three shorterfingers 144-4 contact the inside edge of disk 81-4, and three longerfingers 145-4 contact the inside edge of disk 82-4. Shorter fingers144-4 and longer fingers 145-4 apply radial forces to disks 81-4 and82-4, respectively, and provide a radial clamping function similar tofingers 12-4 in clamp 10-4. If desired, the number of fingers 144-4 and145-4 may be increased.

Magnetic recording disk 10 comprises a thin film surface, withcoercivity greater than 1500 Oe, coated with materials such as Co--Ni orCo--Cr--Ta alloys, applied to both sides of a rigid substrate by methodssuch as RF sputtering or plating. The substrate used with magneticrecording disk 10 is preferably about 0.445 mm thick, with very flat,smooth, surfaces and with good mechanical rigidity. Examples of suitablesubstrate materials are aluminum alloys, glass and ceramic materials.Disk 10 has an outer diameter of about 33.5 mm, a center hole 13 with adiameter of about 10 mm. The data zone utilized is positioned betweenthe radii of 9.4 mm and 15.5 mm.

Magnetic read/write transducers 5, one supported on load beam 14-1 andone on 14-2, are positioned above the recording and playback surface ofrigid disk 10 utilizing rotary actuator assembly 15, which will bedescribed more fully during the detailed description of that assembly inconnection with the drawing FIG. 5A. A rotary inertial latch assembly asdescribed and claimed in U.S. Pat. No. 5,189,576, issued Aug. 21, 1992,more fully identified above, may be utilized to prevent the unwantedmovement of the magnetic heads across the surface of the disk when thedrive is bumped or jarred. In FIG. 1, an alternate construction of aninertial latch mechanism is illustrated. Inertial latch assembly 16 inFIG. 1 will be more fully described and illustrated in connection withother figures. Rotary inertial latch assembly 16 is fully described inU.S. patent application Ser. No. 07/765,353 referred to above.

An embodiment in accordance with the invention is shown in FIG. 50.Inertial latch 100-6 includes an inertial body 101-6 and a sleeve 102-6.A shaft 103-6 is journaled into sleeve 102-6 so as to allow inertiallatch 100-6 to rotate in either direction The other end of shaft 103-6is press fitted into body 10-6B. Shaft 103-6 may also be screwed orbonded into body 10-6B. Inertial latch 100-6 is retained on shaft 103-6by means of a retaining ring (e.g., an "E"-clip) (not shown).

Inertial body 101-6 is formed at one end in the shape of a pawl 104-6which terminates in a hook 104-6a, and shaft 103-6 is positioned on body10-6B so that hook 104-6a is able to engage finger 26-6 of actuator12-6. A pin 105-6 extends upward from the top surface of inertial body101-6. While inertial body 101-6 and sleeve 102-6 are shown as separatecomponents, they could be combined. As indicated by the hatched lines,inertial latch 100-6 is mounted beneath disk 11-6.

Sleeve 102-6 is preferably made of Teflon™ filled polycarbonate and ispress-fitted into inertial body 101-6. Inertial body 101-6 ismanufactured of bronze (85% by mass) filled Nylon II™.

FIG. 51A shows a top view of inertial body 101-6, and FIG. 51B shows aside elevational view of inertial body 101-6 taken from the direction51B shown in FIG. 50.

FIG. 52 is an exploded view of the corner portion of disk drive 10-6where rotary actuator 12-6 and inertial latch 100-6 are positioned.Rotary actuator 12-6 is of the moving coil type, that is, a magnet 106-6is maintained in a stationary position and the movable portion of theactuator 12-6 includes a coil 107-6. Included in actuator 12-6 is abearing assembly 108-6 for rotatably supporting actuator 12-6 aboutpivot shaft 17-6 which is connected to body 10-6B. The flux field isestablished through actuator coil 107-6 through the use of magnet 106-6which is supported on a top plate 109-6 to position the magnet 106-6above the top surface of actuator 12-6. A lower plate 110-6 of themagnet assembly provides the lower portion of the flux path inconjunction with the down turned portion 111-6 of top plate 109-6. A tab109-6a of top plate 109-6 serves as a stop for pin 105-6, therebypreventing inertial latch 100-6 from rotating too far in a clockwisedirection. Inner crash stop assembly 112-6 is positioned between topplate 109-6 and lower plate 110-6. Inner crash stop assembly 112-6prevents the rotation of actuator 12-6 beyond a predetermined innertravel to prevent the read/write transducer heads from leaving thesurface of the disk or hitting other HDA components.

FIGS. 53A and 53B illustrate top and cross-sectional views,respectively, of sleeve 102-6. FIG. 53B is taken through section 53B asindicated in FIG. 53A.

Sleeve 102-6 has formed in it two vertical channels 113-6 and 114-6,respectively, which extend from the top surface of sleeve 102-6 to acircular channel 115-6 which is formed in the interior of sleeve 102-6.Sleeve 102-6 also has a radial slot 116-6 formed in its top surface. Acircular spring 117-6 is inserted into circular channel 115-6. Circularspring 117-6, as shown in FIGS. 54A and 54B, has at one end a hook 118-6and at the other end a lateral arm 119-6.

When circular spring 117-6 is inserted into circular channel 115-6, hook118-6 extends up through vertical channel 114-6 and the end of hook118-6 is placed in radial slot 116-6, thereby securing circular spring117-6 within sleeve 102-6. A finger 115-6a defines a narrow gap 115-6band keeps spring 117-6 from slipping out of channel 115-6.

As shown in FIG. 53A, lateral arm 119-6 engages a wall 120-6 of body10-6B. Thus, as inertial latch 100-6 is rotated in a counterclockwisedirection, circular spring 117-6 is placed in tension and exerts aclockwise torque on inertial latch 100-6.

When disk drive 10-6 incurs a clockwise rotational shock, in the mannerdescribed above the rotational inertia of inertial latch 100-6 overcomesthe torque of circular spring 117-6 and causes inertial latch 100-6 torotate in a counterclockwise direction with respect to body 10-6B. Hook104-6A therefore engages finger 26-6 of actuator 12-6 and preventsactuator 12-6 from rotating so as to bring magnetic head 14-6 intocontact with disk 11-6. When the shock has passed, circular spring 117-6takes over and brings inertial latch 100-6 back to its normal position,where pin 105-6 engages tab 109-6A (see FIG. 52).

A second embodiment in accordance with the invention is shown in FIG.55. Inertial latch 200-6 has an arm 201-6 and a pawl 202-6. Arm 201-6ends in a contact surface 203-6, and pawl 202-6 ends in a hook 204-6.Inertial latch 200-6 is rotatably mounted on a shaft 205-6, which ispressed into body 10-6C. Shaft 205-6 may also be screwed or bonded intobody 10-6C. An outer crash stop block 206-6 is pinned to body 10-6C in aposition between arm 201-6 and pawl 202-6. Outer crash stop block 206-6has attached to it an outer crash stop 207-6, which is positionedopposite finger 26-6 so as to prevent actuator 12-6 from rotating toofar in a clockwise direction.

FIGS. 66A and 66B show top and side elevational views, respectively, ofinertial latch 200-6. To maximize the rotational inertia of inertiallatch 200-6 while minimizing its total mass, the central area ofinertial latch 200-6 (shown by the cross hatching in FIG. 56A) has areduced thickness as compared with the outer areas.

FIG. 57 illustrates a detailed top view of inertial latch 200-6 asmounted. A whisker spring 208-6 is placed on top of inertial latch200-6. In the embodiment shown, whisker spring 208-6 has a circularcross section 0.005 inches in diameter, but it need not have a circularcross section. A leaf spring may be substituted for whisker spring208-6. Whisker spring 208-6 fits into a groove 209-6 near the top ofshaft 205-6. This is shown in FIG. 58, which is a side elevational viewof inertial latch 200-6 taken through cross section 58 shown in FIG. 57.One end of whisker spring 208-6 is fitted into a cored area 210-6 ininertial latch 200-6. The other end of whisker spring 208-6 is insertedinto a slot 211-6 of which is machined into body 10-6C. The relativepositions of cored area 210-6, shaft 205-6 and slot 211-6 are arrangedsuch that whisker spring is pretensioned and urges inertial latch 200-6in a clockwise direction, bringing contact surface 203-6 into contactwith outer crash stop block 206-6. The seating of whisker spring 208-6in groove 209-6 retains inertial latch 200-6 on shaft 205-6. Inertiallatch 200-6 may also be retained on shaft 205-6 by means of a retainingring (e.g., an "E"-clip) .

Inertial latch 200-6 is normally in the position shown in FIG. 57. Whendisk drive 10-6 experiences a clockwise rotational shock, inertial latch200-6 rotates in a counterclockwise direction until the inner edge ofpawl 202-6 comes into contact with a surface of outer crash stop block206 (see FIG. 59). In this position hook 204-6 will engage finger 26-6so as to prevent actuator 12-6 from rotating. Once the shock has passed,whisker spring 208-6 will urge inertial latch 200-6 towards its normalposition, where surface 203-6 makes contact with outer crash stop block206-6. The placement of whisker spring 208-6 on top of inertial latch200-6 minimizes friction and thereby maximizes the response speed ofinertial latch 200-6 to a rotational shock.

The ease of assembling this embodiment makes it particularly attractive.As shown in FIG. 60, inertial latch 200-6 is simply fitted onto shaft205-6 and whisker spring 208-6 is fitted into cored area 210-6, groove209-6 and slot 211-6. Inertial latch 200-6 is preferably installedbefore outer crash stop block 206-6, and a surface 213-6 of body 10-6Cacts as a stop for inertial latch 200-6 during installation. Installinginertial latch 200-6 in this sequence may make it easier to installactuator 12-6.

Read/write transducers 5 which are supported on the ends of load beams14-1 and 14-2 are dynamically loaded and unloaded from the surfaces ofmagnetic disk 10 through the use of a lift tab 17 which is integrallyformed at the free end of load beams 14-1 and 14-2. The details of loadbeams 14-1 and 14-2 and lift tab 17 are described more fully hereinafterin connection with FIGS. 6A-6I. Cam assembly 18, in conjunction withload tab 17, on each of the lift beams provide for the dynamic loadingand unloading of write/read transducers 5. As pointed out above, analternative to the dynamic head loading illustrated in the figuresherein is the use of the dynamic head load structure in the abovedescribed U.S. patent application Ser. No. 07/629,957, as well as usingcontact start stop techniques.

Feedthrough connector 19 mounted on baseplate 6 includes a plurality ofterminals 20 which extend through baseplate 6 and provide connectionbetween the electronics internal of the HDA portion of disk drive 1 andthose external to the HDA. For example, printed circuit board 2 includesvarious electrical circuitry, which will be more specifically describedhereinafter in connection with FIGS. 7A and 7B. Within the housing ofmicrominiature hard disk drive 1, read/write preamp circuitry isincluded on read/write integrated circuit chip 21, and the signals toand from read/write preamp IC chip 21 are provided to the externalportion of hard disk drive 1 utilizing connector 22 which interfaceswith pins 20 on feedthrough connector 19. Signals to and from spin motor3 are provided via flat cable 23, one end of which is connected to spinmotor 3 and the other end of which connected to connector 24. Connector24 plugs onto some of pins 20 of feedthrough connector 19 to passsignals to and from the exterior of the housing of miniature hard diskdrive 1.

Included in rotary actuator assembly 15 is an inner crash stop assembly25 which provides the crash stop function to prevent read/writetransducer heads 5 from crashing into the inner portion of the rotarydisk and spindle and thereby damaging the heads and/or the magneticrecording surface. Inner crash stop assembly 25 is illustrated in detailin FIG. 3C which will be described later herein.

The interior of hard disk drive 1 is enclosed utilizing top cover 26, asuitable gasket (not shown in FIG. 1). Top cover 26, which is composedof die cast aluminum, is held securely in place on baseplate 6 utilizingsuitable mounting screws, not shown. In a stacked configuration, printedcircuit board 2 is supported beneath baseplate 6 utilizing suitablefastening means (not shown). Gasket 27 is illustrated in thecross-sectional view of microminiature hard disk drive 4, shown in FIG.4.

Female connector 28 on printed circuit board 2 is positioned directlybeneath the lower portions (not shown) of pins 20 to couple signals fromthe interior of hard disk drive 1 to the printed circuit board 2. Maleconnector 29 provides direct connection from the HDA of disk drive 1 andthe electronics located on printed circuit board 2 to the system withwhich rigid disk drive 1 and its associated electronics are connected.The interface between hard disk drive 1 and the system in which it willbe used may take various forms, such as SCSI, microchannel or AT Bus. InFIG. 1, integrated circuits 30 and 31 on printed circuit board 2, aswell as others not shown, implement the external drive electronics whichis illustrated in block diagram form in FIG. 7B.

Referring to FIG. 2A, a top plan view of hard disk drive 1 stacked aboveprinted circuit board 2 is illustrated. The width of hard disk drive 1is measured from peripheral edge 32 to peripheral edge 33 isapproximately 35 mm. The length of hard disk drive 1, as measured fromperipheral edge 34 to rear peripheral edge 35 is approximately 50.8 mm.In FIG. 2A, hard disk drive and its associated printed circuit board 2are illustrated in a stacked configuration in which printed circuitboard 2 is directly beneath hard disk drive 1. As pointed out earlierherein, the side to side rear dimensions in the stacked version, asmeasured from rear peripheral edge 33 of hard disk drive 1 to left edge36 of printed circuit board 2 is approximately 41 mm.

FIG. 2B is a view taken along lines 2B--2B of FIG. 2A. The height ofhard disk drive 1 and printed circuit board 2 mounted in the stackedrelationship, with the height measured from top surface 37 of hard diskdrive 1 to the lower surface 38 of printed circuit board 2 isapproximately 6.3 mm. Tall electrical components can be placed onprinted circuit board 2 to take advantage of cavities or pockets inbaseplate 6, thereby facilitating the low profile packaging.

FIG. 2C is a view taken along lines 2C--2C of FIG. 2A.

Referring to FIG. 2D, a top plan view of an alternative embodiment ofthe present invention is illustrated. In FIG. 2D, a disk drive inaccordance with the present invention is enclosed within a resilientcover 39 which encases and provides shock mount protection for the harddisk drive included within resilient cover 39. Resilient cover 39includes gripping surface 40 to facilitate easy insertion and removal ofthe package into a plug relationship with a host computing device. Forexample, as illustrated in FIG. 2F, which is a view taken along lines2F--2F in FIG. 2D, electrical connector 41 which includes a plurality ofpins, and extends from one edge of the disk drive included withinresilient cover 39, provides electrical connection between the hard diskdrive included within the cover and the host computing device whichcommunicates with the removable disk drive enclosed within cover 39.

FIG. 2E is a view taken along lines 2E--2E of FIG. 2D, and illustratesin side view the hard disk drive which is enclosed within cover 39. Theresilient cover 39 and the pluggable feature of the disk drive aredescribed and claimed in U.S. patent application Ser. No. 07/765,349 ofJ. Morehouse et al. filed Sep. 25, 1991, issued Sep. 27, 1992 as U.S.Pat. No. 5,149,048, and entitled "Shock Absorbent Mounting ArrangementFor Disk Drive Or Other Component ", which is incorporated herein byreference in its entirety.

Referring to FIGS. 43 and 44, an architecture of the present inventionincorporates a head-disk assembly (HDA) which comprises a spindle motor10-5, an information bearing disk 20-5, and one or more read/write heads30-5 which are disposed on an actuator 40-5 to read from or write to thedisk 20-5.

The read/write head 30-5 is disposed on arm 50-5 which is fixedlydisposed on an actuator 40-5. The actuator 40-5 pivots about a shaft45-5 to move the read/write head 30-5 over a sweep angle φ between anouter periphery 23-5 and an inner periphery 24-5 of the disk 20-5.

The spindle motor 10-5 is preferably a low-profile DC brushless motor asshown in FIG. 43. The spindle motor 10-5 is comprised of a motor housing11-5 within which is disposed a stator. The stator comprises magneticlaminations 13-5 and coil windings 14-5. A rotor 15-5 includes a rotorshaft 16-5 which is rotatably disposed on the spindle motor 10-5 bymeans of spindle bearings 60-5. The rotor 15-5 further includes a cap31-5 connected to one end of the rotor shaft 16-5, a cylindrical portion32-5 connected at a first end to the cap 31-5, the cylindrical portion32-5 being coaxial with the rotor shaft 16-5, and a disk-shaped portionconnected to a second end of cylindrical portion 32-5. Disposed on theouter periphery of the disk-shaped port the rotor 15-5 are rotor magnets18-5. On an upper surface 28-5 of the disk-shape portion of the rotor15-5 is machined a disk mounting surface 27-5. The disk mounting surface27-5 provides a relief for machining purposes for precisely positioningthe disk 20-5 relative to the read write head 30-5 and for applying auniform force on a lower (first) surface 21-5 of the disk 20-5. The diskmounting surface 27-5 separates the lower surface 21-5 of the disk 20-5from the upper surface 28-5 of the disk-shaped portion of the rotor 15-5by a minimal distance of approximately 0.13 mm. Therefore, the disk 20-5substantially abuts the disk-shaped portion of rotor 15-5.

Disposed on the disk mounting surface 27-5 is the disk 20-5, the disk20-5 being held against the disk mounting surface 27-5 by means of aclamp 19-5 having a second diameter. Similar to the mounting surface27-5, the clamp 19-5 has a precision surface to apply a uniform clampingforce on an upper (second) surface 22-5 of the disk 20-5.

The architecture of the present invention is characterized in that thelower surface 21-5 of the disk 20-5 substantially abuts the uppersurface 28-5 of the rotor 15-5. In addition, the architecture of thepresent invention is characterized in that the lower surface 21-5 of thedisk 20-5 is not used for information storage; that is, the read/writehead 30-5 incorporated into a disk drive device incorporating thearchitecture of the present invention are located above a plane Pdefined by the lower surface 21-5 of the disk 20-5. Finally, thearchitecture of the present invention is characterized in that the disk20-5 is used as a shield for information read from or written to theupper surface 22-5 of the disk 20-5 and neither a ferrite nor othershield is required.

The architecture of the present invention facilitates modifications tothe spindle motor 10-5 which result in a low-profile design well suitedfor disk drive devices incorporating disks having an outer diameter of1.8 inches or less. There is essentially no space, similar to the spacet (discussed in the Background) between the upper surface 28-5 of therotor 15-5 and the lower surface 21-5 of the disk 20-5, as is requiredin the prior art low-profile architecture. Instead, the flat uppersurface 28-5 of the rotor 15-5 substantially abuts the lower surface21-5 of the disk 20-5. In addition, the outer diameter of the spindlemotor 10-5 is not limited as in the prior art low-profile architecture.Since motor power is substantially related to motor volume, the spindlemotor may be made with a larger diameter and lower profile withoutsacrificing power. For use with a 1.8 inch disk, the spindle motordiameter may be approximately 31 mm, the thickness reduced toapproximately 5.0 mm. Because there is essentially no space between thedisk 20-5 and the motor 10-5, the minimum thickness of a single disk,one-head HDA incorporating the present architecture is approximately 7.1mm (adding 1.5 mm for the necessary read/write head clearance). This isapproximately one half of the 13.6 mm thickness of a typical prior artone-disk, two-head HDA.

In addition a spindle motor with a larger diameter and thinner profileis superior to smaller diameter motors in that they produce a largertorque constant, lower rotational jitter, increased inertia and allowthe motor bearings to be placed inside the stator to further reduce HDAheight.

In addition to the lower profile, an HDA incorporating the architectureof the present invention provides an additional advantage over the priorart low-profile architecture in that the read/write head 30-5 disposedover the upper surface 22-5 is capable of accessing information trackscloser to the rotor shaft 16-5. The accessible disk storage space isincreased over the prior art low-profile in that the sweep angle φ isnot restricted by the lower surface 21-5 of the disk 20-5, as in theprior art. The amount of additional information track storage space perdisk surface accessed by the read/write head 30-5 is approximately 40%greater than the storage space accessed using the preferred motor sizeof the prior art low-profile architecture and disks having the same sizeand density. Therefore, a greater storage capacity per disk surface isachieved.

Also characteristic of the present architecture is a reduction of thenumber of read/write heads 30-5 needed to access substantially the sameor more information surface on the disk 20-5 and any additional diskmounted above the disk 20-5. The reduction in the number of read/writeheads also reduces the spindle motor starting torque in the case of acontact start-stop head/disk interface, thereby conserving battery powerin portable applications. A similar advantage is achieved in the case ofdynamic loaded heads where the actuator load/unload torque is alsoproportionally reduced.

Also characteristic of the present architecture is that the rotor 15-5acts as shielding member for electrical and magnetic fields emanatingfrom the spindle motor 10-5 (FIG. 44). The disk 20-5 acts as a furthershielding member for the upper surface 22-5, which is used forinformation storage, by means of the magnetic disk coating on the lowersurface 21-5 and eddy current shielding due to the conductive disksubstrate. Therefore, no ferrite shield is necessary as in the typicalprior art architecture.

Comparison between the HDA of FIG. 43 and the one typical disk, two headprior art HDA yields the following results. First, as discussed above,the height of the HDA of FIG. 43 is approximately one half the height ofthe prior art HDA. Second, because the rotor 15-5 and disk 20-5 act asshields, it is less likely a read/write error will occur in the HDA ofFIG. 43 than in the prior art HDA. Finally, because the read/write head30-5 accesses 40% more storage area per disk, the single-head HDA ofFIG. 43 provides approximately 70% of the information storage capacityof the two-head HDA. Given the lower-profile and greater shieldingprovided with the present invention, a 30% decrease in storage capacityis an acceptable trade-off in some situations.

A two-disk HDA according to the present invention is shown in FIG. 45.The two-disk HDA comprises a motor 10-5 incorporating an extended rotorshaft 16-5(2). A modified rotor 15-5(2) is press-fitted onto the rotorshaft 16-5(2). The modified rotor 15-5(2) includes a cap 31-5(2)connected to one end of the rotor shaft 16-5(2), a cylindrical portion32-5(2) connected at a first end to the cap 31-5(2), the cylindricalportion 32-5(2) being coaxial with the rotor shaft 16-5(2), and adisk-shaped portion connected to a second end of the cylindrical portion32-5(2). A first disk 20-5 is clamped to the upper surface 28-5 of thedisk-shaped portion of the rotor 15-5(2) as in the single-diskembodiment shown in FIG. 43. In addition, a top cap 4540 is mounted bymeans of a screw 4541 to the top of the rotor shaft 16-5(2). The top cap4540 has a depending portion 4542 which defines a second mountingsurface 4527. A second disk 25-5 is clamped to the second mountingsurface 4527 by means of a second clamp 4519. Second and thirdread/write heads 4530 and 4531 are mounted to arms (not shown) of theactuator (not shown) and disposed adjacent the lower surface 21-5(2) andupper surface 22-5(2) of second disk 25-5. In a similar manner, one ormore additional disks may be mounted to the rotor of FIG. 45.

Since both sides of the one or more additional disks are used forinformation storage, the architecture of the two-disk HDA of FIG. 45 ischaracterized in that, if the number of information bearing disksmounted on the spindle motor is designated as n, the number ofread/write heads used is defined by the equation 2n-1.

The architecture of the two-disk HDA of FIG. 45 is further characterizedin that, where first disk 20-5 and the one or more additional disks 25-5are incorporated into an HDA with the first disk 20-5 disposed adjacentthe spindle motor 10-5, the lower surface 21-5 of the first disk 20-5defining a plane P (shown in side view in FIGS. 45 and 46), oneread/write head 30-5 being disposed adjacent the first disk 20-5, andtwo read/write heads 4530 and 4531 being disposed adjacent each of theone or more second disks 25-5, all of the read/write heads are disposedonly on a side of the plane P opposite to a side containing the spindlemotor 10-5.

Assuming the thickness of the motor 10-5 shown in FIG. 45 isapproximately 5 mm, as measured from a bottom surface of the motor 10-5to the upper surface 28-5, the height of the two-disk embodiment iscalculated as follows. The distance between the upper surface 22-5 ofthe first disk 20-5 and the lower surface 21-5(2) of the second disk isapproximately two times the space t, or approximately 3.0 mm. Anadditional 1.5 mm is necessary above the second disk 25-5 for disposingthe read/write head 4531. Finally, assuming the disk thickness is 0.6mm, the height of the two-disk HDA of FIG. 45 is approximately 10.7 mm.

The two-disk HDA of FIG. 45 yields significant advantages over thetwo-disk, four-head prior art HDA shown in FIG. 49A. The reduction ofmotor height by approximately one-half and the elimination of the spacebetween the motor and the lower disk 20-5 yields an approximate 6.5 mmreduction in thickness over the prior art HDA of FIG. 49A. Moreover,because the read/write head 30-5 accesses information tracks closer tothe rotor shaft 16-5(2), the sweep angle φ (shown in FIG. 44) of thetwo-disk HDA of FIG. 45 is significantly larger than the sweep angle θof the prior art embodiment of FIG. 49A. Accordingly, a read/write headaccesses 40% more disk surface area in the HDA of FIG. 45 over the HDAof FIG. 9A. Therefore, the HDA of FIG. 45 has 1.4 times the informationstorage capacity per disk surface over the prior art HDA of FIG. 49A.Accordingly, the three disk surfaces of the HDA of FIG. 45 provide astorage capacity which is approximately 4% greater than the four disksurfaces of the prior art HDA of FIG. 49A.

The comparison between the HDA of FIG. 45 and prior art HDA of FIG. 49Ais summarized in the following table:

    ______________________________________                                                    Prior Art Two-                                                                            Two-Disk Present                                                  Disk Architecture                                                                         Architecture                                                      (FIG. 49A)  (FIG. 45)                                             ______________________________________                                        Disk Storage Area                                                             Outer Data Radius;                                                                          21.56 mm      21.56 mm                                          Inner Data Radius:                                                                          14.80 mm      11.11 mm                                          Relative Data Capacity                                                                      1.0           1.39                                              per Disk Surface;                                                             Number of Disks:                                                                            2             2                                                 Number of Available                                                                         4             3                                                 Data Surfaces:                                                                Total Relative Storage                                                                      4.0           4.17                                              Capacity:                                                                     Capacity Ratio:                                                                             1.0           1.0425                                            HDA Thickness                                                                 Motor Thickness                                                                             10 mm         5 mm                                              Total Disk Thickness                                                                        1.2 mm        1.2 mm                                            (Approximately 0.6                                                            mm per disk)                                                                  Number of Heads                                                                             4             3                                                 Total Space needed for                                                                      6 mm          4.5 mm                                            heads (Approximately                                                          1.5 mm per head)                                                              Approx. HDA thickness:                                                                      17.2 mm       10.7 mm                                           ______________________________________                                    

Because of the approximate reduction in thickness of one-third and theslight increase in storage capacity, the embodiment shown in FIG. 45 ispreferable to the prior art HDA of FIG. 49A In addition furtherincreases in storage capacity are achieved with the three-disk,five-head HDA shown in FIG. 46, as compared with the three-disk, sixhead prior art HDA of FIG. 49B.

FIGS. 47A-47H illustrate various simplified HDAs according to thepresent invention and the prior art architecture. FIGS. 47A-47H, inconjunction with the below table, are provided to better illustrate theadvantages of the present architecture over the prior art low-profilearchitecture. In addition, FIGS. 47C and 47G illustrate two otherpossible embodiments according to the architecture of the presentinvention. For simplification purposes, the height of the prior artmotors in FIGS. 47A, 47D and 47F are assumed to be four times the spacet, or 6 mm. The motors of the present embodiments shown in FIGS. 47B,47C, 47E, 47G and 47H are all assumed to be two times the space t, or 3mm. In addition, the space taken up by the thickness of the disks isdisregarded. Finally, the storage capacity per disk surface accessed bythe read/write heads of the present embodiments is assumed to be 1.4times the storage capacity per disk surface accessed in the prior artHDAs.

With the above assumptions, comparisons between the prior art HDAs andthe HDAs according to the present invention are listed in the belowtable. Note that the height ratio is the thickness of the "HDA2" dividedby the thickness of "HDA1". Similarly, the capacity ratio is thecapacity of "HDA2" divided by the capacity of "HDA1".

    __________________________________________________________________________    Comparison                                                                             Thickness                                                                           Capacity                                                                            Thickness                                                                           Capacity                                                                             Height                                                                            Capacity                                HDA1 vs. HDA2                                                                          HDA1  HDA1  HDA2  HDA2   Ratio                                                                             Ratio                                   __________________________________________________________________________    47A vs. 47B                                                                            6t    2 × 1 = 2                                                                     3t    1 × 1.4 = 1.4                                                                  1/2 0.7                                     47A vs. 47C                                                                            6t    2     4t    2.8    2/3 1.4                                     47D vs. 47E                                                                            8t    4     5t    4.2    5/8 1.05                                    47D vs. 47G                                                                            8t    4     6t    5.6    3/4 1.4                                     47F vs. 47H                                                                            10t   6     7t    7.0    7/10                                                                              1.16                                    __________________________________________________________________________

As noted from the above table, comparison between two-head prior art HDAof FIG. 47A and the two-head HDA of FIG. 47C yields an increase instorage capacity of approximately 40%, while requiring one-third lessHDA thickness. Similarly, a comparison between four-head prior art HDAof FIG. 47D and the four-head HDA of FIG. 47G yields an increase instorage capacity of approximately 40% while requiring one-fourth lessHDA thickness.

One skilled in the art would recognize from the embodiments shown inFIGS. 47A-47H that many variations are possible in the number of headsversus the number of disks in order to meet specific requirements. Forinstance, the HDAs of FIGS. 48A and 48B illustrate a two-disk, two-headHDA, and a three-disk, three-head HDA, respectively, according to thepresent invention. Each of these HDAs would provide approximately 70% ofthe storage capacity of the two- and three-disk HDAs of FIGS. 49A and49B, but would require much less HDA thickness.

Microminiature hard disk drive 1 is illustrated in FIG. 3A in the topplan view, with the top cover 26 removed for illustration of thecomponents. In FIG. 3A, load beam 14-1 and its associated read/writetransducer is illustrated in a parked position off the disk and in itsinnermost position of travel. In the hard disk drive 1 structure dynamichead loading is utilized and therefore when the disk drive is powereddown and, i.e., not rotating, load beams 14 and 14-1 and 14-2 (notshown) one moved to the position illustrated where lift tab 17 is in aparked position on cam assembly 18 to prevent the read/write transducerheads from interfering with or damaging the disk surface. As will beappreciated by referring to the drawing, when the actuator has moved theheads to the unloaded position, projection 42 from coil supportextension 43 is positioned for engagement with the free end of inertiallatch 16' in the event of a shock to the drive. In the event of a shock,inertial latch 16' will move such that its free end will engage withprojection 42 on actuator coil support extension 43 and prevent theactuator, and accordingly the read/write heads, from moving across thesurface of the disk. The details of the rotary actuator and body aredescribed and disclosed more fully hereinafter with respect to FIG. 5Afor the dynamic head loading version and FIG. 5B for the contactstart/stop version of the drive. It will also be appreciated by viewingFIG. 3A that inner crash stop assembly 25 (which will be described fullyhereinafter in the explanation of FIG. 3C) prevents the actuator frommoving more fully then the most inwardly disclosed position in FIG. 3A.Also illustrated in FIG. 3A is read/write analog integrated circuit 21and connector 22 which is positioned over feed through connector 19 (notshown since it is beneath connector 22). In the same general area, itwill also be recognized that flat cable 23 and connector 24, whichprovides electrical connection from the spin motor to the pins on feedthrough connector 19, is also illustrated. Flex cable 44 is utilized totransmit the signals from the read/write recording head to read/writepreamp chip 21 is illustrated in the lower left-hand corner of drive 1.Also included in the HDA housing is recirculating filter 150 to filterthe air within the interior of the housing.

Details of the rotary actuator mechanism will best be appreciated byreference to FIG. 5A which is an exploded view of the corner portion ofhard disk drive 1 where the rotary actuator is positioned. Rotaryactuator assembly 15 is of the moving coil type, that is a magnet ismaintained in a stationary position and the movable portion of theactuator includes coil 45 which is supported on coil support extension43 of actuator body 46. Included in actuator body 46 is a bearingassembly 47 for rotatably supporting actuator body 46 about pin 47 whichis connected to base plate 6. Also illustrated in FIG. 5A is upper loadbeam 14-1 and lower load beam 14-2 which are rigidly supported onactuator body 46 for rotation and positioning of read/write transducers5 above the surface of disk 10. It will also be noted that lift tabs 17extend from the free ends of load beams 14-1 and 14-2. The flux field isestablished through actuator coil 45 through the use of magnet 48, whichis supported on top plate 49 to position the magnet 48 above the topsurface of actuator 45. Lower plate 50 of the magnet assembly providesthe lower portion of the flux path in conjunction with the down turnedportion 51 of top plate 49. Inner crash stop assembly 25 with preloadpin 52 is positioned between top plate 49 and lower plate 50. As pointedout above, the inner crash stop prevents the rotation of rotary actuatorbeyond a predetermined inner travel to prevent the read/write transducerheads from travelling into an unburnished portion of the disk surface orhitting HDA components. Inertial latch 16-1 is supported for rotation onbase plate 6 by inertial lock sleeve 53, the inner portion of which issupported on pin 54 and the outer portion of which is fitted within theaperture of inertial latch 16-1. Further details of the rotary latchmechanism are found in the above-identified U.S. Pat. No. 5,189,576 ofMorehouse et al. issued Feb. 23, 1993and U.S. patent application Ser.No. 07/765,353.

Better appreciation of the cam assembly 18 will be gained by referenceto FIG. 5C. Referring concurrently to FIGS. 3A and FIG. 5C, it will beappreciated that lift tabs 17 in cooperation with cam surface 18-1cooperate to move the load beams, and accordingly the read/writetransducer heads, above the surface of the disk when the rotary actuatoris moved into the unloaded position as illustrated in FIG. 3A where lifttab 17 is at a rest position above surface 18-1 of cam assembly 18. Thelower cam surface (not shown) of cam assembly 18 is substantiallyidentical to the upper cam surface 18-1, and therefore in cooperationwith load tip 17 on load beam 14-2 moves the lower read/write transduceraway from the lower surface of disk 10.

Inner crash stop assembly 25 is illustrated in a highly enlarged scaledrawing in FIG. 3C. For this illustration, top plate 49 is not shown inFIG. 3C, and additionally a portion of the top of inner crash stop block55 has been removed. Inner crash stop assembly 25 includes inner crashstop spring 56 which is positioned between legs 57 and 58 of inner crashstop block 55 and the inner peripheral surface of preload pin 52. Aswill be appreciated by reference to FIG. 3C, inner crash stop spring 56is preloaded by the inner peripheral surface of pin 52 in combinationwith legs 57 and 58. As illustrated in FIG. 3C, actuator body 46includes inner crash stop contact tab 59 which extends from the edge ofactuator body 46 and as illustrated by the arrows in FIG. 3C comes intocontact with contact inner crash stop spring 57 when the actuator ismoved to position the heads toward the innermost portion of magneticdisk 10. The contact between inner crash stop contact tab 59 and innercrash stop spring 56 cushions and stops the inner travel of the actuatorto prevent the heads from hitting other HDA structural elements.

Referring to FIG. 3B microminiature hard disk drive 4, which isimplemented in the contact start/stop version, is illustrated in topplan view. By comparing FIG. 3B with 3A, it will be appreciated that anumber of common structural elements exist in the dynamic head loadingversion illustrated in FIG. 3A and the contact start/stop versionillustrated in FIG. 3B. Of course, in contact start/stop version thelift tabs in the cam assembly is not required since the read/writetransducers take off and land on the surface of a recording disk 60.Recording disk 60 differs from recording disk 10 used in hard disk drive1 in that a take off and landing zone, bonded by dashed lines 61 and 62(3B) on the surface of recording disk 60, is provided. Other portions ofhard disk drive 4 which are also commonly used in hard disk drive 1includes inner crash stop assembly 25, flat cable 23 which is coupledbetween connector 24 in the spin motor, connector 22 and read/writepre-amp integrated circuit chip 21. Also illustrated in flex cable 44. Arotary latch may also be utilized with this embodiment, although one isnot shown in this figure.

In FIG. 5B a highly exploded and enlarged view of the actuator assembly15 used in microminiature hard disk drive 4 is illustrated. As will beappreciated by reference to the figure, various common elements are usedin this actuator assembly which are in common with actuator assemblyillustrated in FIG. 5A for the dynamic headload versions. Commonstructural elements are indicated by the same reference characters asused in previous figures. By reference to FIG. 5B, it will of course beappreciated that upper load beam 63-1 and lower load beam 63-2 do notinclude loading tabs since none are required for the contact start-stopversion. Lift tabs may be used in the contact start-stop version duringinitial assembly head loading operation. However, the read/writerecording heads 5 could be different than those utilized in the dynamichead loading version.

To better appreciate the explanation of the structural characteristicsof hard disk drive 4, concurrent reference with FIG. 3B and FIG. 4(which is a cross-sectional view of hard disk drive 4 taken along thelines 4--4 in FIG. 3B) will be helpful. Rigid disk 60 is supported forrotation in baseplate 6 by a brushless DC spin motor. A detaileddescription of one brushless DC spin motor suitable for use with thisdisk drive is included in copending above-described U.S. patentapplication Ser. No. 07/630,110. Portions of this motor will also bedescribed herein for the purposes of illustration with regard to harddisk drive 4. Referring to FIGS. 3B and 4, the brushless DC motorincludes a stator portion having three lamination portions 64, each ofwhich has windings 65. The stator portion is supported. on baseplate 6.Rotor 66 is rigidly affixed to shaft 11 which is supported in baseplate6 utilizing a bearing assembly, the bearings of which are indicated at67. Permanent magnet ring 68 is supported in operative relationship tothe plurality of lamination portions 64 and windings 65, with permanentmagnet ring 68 being supported on lower portion 69 of rotor 66. Rigiddisk 60 is supported on rotor 11 for rotation therewith by clamp ring 12which is pressfit onto rotor 11. The details of the start-up commutationas well as direction detection for the spin motor fully described in theabove referenced U.S. patent application Ser. No. 07/630,470.

Load beams 63-1 and 63-2 of actuator assembly 65 pivots about center ofrotation 70. Load beam 63-1 supports at its free end, adjacent to disk60, in this Figure, read/write transducer 5.

Referring to FIG. 4, this cross-sectional view illustrates theutilization of down load beam 63-1 which supports read/write transducer5 which is positioned above the upper surface of hard disk 60. Alsoillustrated in FIG. 4 is up load beam 63-2 which supports read/writetransducer 5 which is positioned adjacent to the lower surface of rigiddisk 60. The respective terms "up" and "down" with regard to the loadbeams are utilized to indicate the operative orientation of theread/write transducer associated with the load beam. For example, download beam 63-1 is so named because the read/write transducer associatedwith that load beam is facing downwardly as viewed from the position ofhard disk drive 4 in FIG. 3B. Similarly, up load beam 63-2 is sodenominated because the read write transducer included on up load beam63-2 is facing upwardly.

As is best illustrated in FIG. 4, upper load beam 63-1 and lower loadbeam 63-2 are supported for rotation about center of rotation 70 byactuator body 46. Actuator body 46 is rotatably supported on baseplate 6by a suitable bearing assembly 47 which includes actuator bearings 71.It will of course be recognized by those skilled in the art that thehead positioning mechanism used in hard disk drive 4 is of the movingcoil rotary actuator type. Actuator coil 45 is provided with appropriatedriving signals to position the read-write recording elements over theappropriate track based on commands received from actuator drivercircuits which will be described hereinafter. Permanent magnet 48 inconjunction with lower plate 50 and upper plate 49 provide a magneticflux field across actuator coil 45. To reduce the height of head diskassembly 1, a single permanent magnet (permanent magnet 48) is utilizedin conjunction with upper plate 49 and return plate 50. The physicalsize and shape of actuator coil 45 is determined in part by theavailable clearance and space within baseplate 6, and will beappreciated by reference to FIGS. 3B, 4 and 5B. From an electricalstandpoint, the number of turns and the gauge of the wire used inactuator coil 45 are provided such that the resistance of actuator coil45 is approximately the same as the resistance of the spin motor. It isimportant that this relationship be established since during power downthe back EMF of the spin motor in dynamic head load-unload version ofhard disk drive 1 is used to drive the actuator coil and move the headgimbal assembly into the unloaded position as illustrated in FIG. 3A.This equal resistance relationship is also important because for a givencoil geometry the unload torque generated is at a maximum when the wiresize and number of turns produces a coil resistance equal to theresistance of the series combination of the two spin motor windings pluscircuit and trace resistances.

To protect the components in hard disk drive 1 and hard disk drive 4from contamination by particles which could among other things, cause ahead crash, top cover 26 is sealed to baseplate 6 by providingappropriate interfitting relationship between top cover 26, baseplate 6and the utilization of a resilient gasket 27 (FIG. 4). Gasket 27 extendsaround the periphery of baseplate 6 as illustrated in FIGS. 6 and 8.Referring to FIG. 4, it will be noted that peripheral edge 72 of topcover 26 extends around the periphery at top cover 26 fits withperipheral edge 73 of baseplate 6. To reduce the electrical interferencefrom spin motor 3 to lower read/write transducer, shield 74 ispositioned on baseplate 6 as illustrated in FIG. 4. Shield 74 ispreferably composed of a high permeability ferrite material which shuntsthe EMI at the frequency of the pass band of the recording channel.Cover 7 is secured to baseplate 6 using suitable fastening means.

The above-described spin motor is controlled by spin control and drivercircuit 74 which is illustrated in block diagram form in FIG. 8. Spincontrol and driver circuit 74 may be implemented an Allegro MicroSystems Inc., part number ULM 8902 denominated "three phase brushless DCmotor drive with back-EMF sensing", which is illustrated in FIG. 8 inblock diagram form. Alternately, the spin control and driver circuit 74may be implemented as described in copending and commonly assigned U.S.patent application Ser. No. 07/630,470 filed Dec. 19, 1990.

As an alternative to the spin motor described in the above-identifiedpatent application, a parallel wound spin motor may be utilized. In aparallel wound spin motor there are two windings on the stator, bothwound in the same direction. With the parallel wound motor, spin motordrive circuit 75, illustrated in FIG. 9, is utilized to start and runthe motor. A description of the operation of spin motor drive circuit 75is as follows.

START MODE:

During start mode more torque is required. The six motor windings areconnected such that 3 motor phases are made with each phase having twowindings in parallel. Also, bipolar drive is used so that two phases areenergized at one time. If desired unipolar drive can be used.

Bipolar Mode

In start mode transistors Q7,8,10,11,13,14 are conducting. This placesmotor windings Phase A1, A2 in parallel, Phase B1,B2 in parallel andPhase C1,C2 in parallel. Transistors Q9,12,15,16,17,18 arenonconducting. Transistors Q1,2,3,4,5 and 6 are toggled in the normalsix step sequence to rotate the motor. The sequence is:

Step 1: Q1 and Q4 are conducting while Q2,3,5 and 6 are non-conducting.Current flows from V_(cc) through Q1, Phase A1,A2, Phase B1,B2 and Q4causing a positive torque to be generated.

Step 2: Q1 and Q6 are conducting while Q2,3,4 and 5 are non-conducting.Current flows from V_(cc) through Q1, Phase A1,A2, Phase C1,C2 and Q6causing a positive torque to be generated.

Step 3: Q3 and Q6 are conducting while Q1,2,4 and 5 are non-conducting.Current flows from V_(cc) through Q3, Phase A1,A2, Phase C1,C2 and Q6causing a positive torque to be generated.

Step 4: Q3 and Q2 are conducting while Q1,3,4 and 6 are non-conducting.Current flows from V_(cc) through Q3, Phase A1,A2, Phase C1,C2 and Q2causing a positive torque to be generated.

Step 5: Q5 and Q2 are conducting while Q1,3,4 and 6 are non-conducting.Current flows from V_(cc) through Q5, Phase A1,A2, Phase C1,C2 and Q2causing a positive torque to be generated.

Step 6: Q5 and Q4 are conducting while Q1,2,3 and 6 are non-conducting.Current flows from V_(cc) through Q5, Phase A1,A2, Phase C1,C2 and Q4causing a positive torque to be generated.

This sequence is used 6 times per revolution.

Unipolar Mode

In start mode transistors Q7,8,10,11,13,14 and 16 are conducting. Thisplaces motor windings Phase A1,A2 in parallel, Phase B1,B2 in paralleland Phase C1,C2 in parallel. Transistors Q2,4,6,9,12,15,17,18 arenon-conducting. Transistors Q1,3 and 5 are toggled in the normal threestep sequence to rotate the motor. The sequence is:

Step 1: Q1 and Q16 are conducting while Q3 and 5 are non-conducting.Current flows from V_(cc) through Q1, Phase A1,A2, Phase B1,B2 and Q16causing a positive torque to be generated.

Step 2: Q5 and Q16 are conducting while Q1 and 3 are non-conducting.Current flows from V_(cc) through Q5, Phase A1,A2, Phase C1,C2 and Q16causing a positive torque to be generated.

Step 3: Q3 and Q16 are conducting while Q1 and 5 are non-conducting.Current flows from V_(cc) through Q3, Phase A1, A2, Phase C1,C2 and Q16causing a positive torque to be generated.

This sequence is repeated six times per revolution.

RUN MODE:

During run mode very little torque is required to run the motor. Onlyone winding is used per phase. Since little torque is used, very littleback EMF is generated thus allowing 3 volts to drive the motor withadequate headroom.

Phase A2,B2 and C2 are not used to deliver torque to the motor. Theyare, however, connected in series so that a back EMF voltage greaterthan that generated by a single winding is developed. Thus transistorsQ7,8,10,11,13,14,16,17 and 18 are off during normal operation.Transistors Q9, 12 and 15 are on all the time. Thus A1 and A2 areconnected in series, B1 and B2 are connected in series and C1 and C2 areconnected in series.

Bipolar Mode

Step 1: Transistors Q1 and Q4 are conducting while Q2,3,5 and 6 arenon-conducting. Current flows from V_(cc) through Q1, Phase A1, Phase B1and Q4 causing a positive torque to be generated.

Step 2: Transistors Q1 and Q6 are conducting while Q2,3,4 and 5 arenon-conducting. Current flows from V_(cc) through Q1, Phase A1, Phase C1and Q6 causing a positive torque to be generated.

Step 3: Transistors Q3 and Q6 are conducting while Q1,2,4 and 5 arenon-conducting. Current flows from V_(cc) through Q3, Phase A1, Phase C1and Q6 causing a positive torque to be generated.

Step 4: Transistors Q3 and Q2 are conducting while Q1,3,4 and 6 arenon-conducting. Current flows from V_(cc) through Q3, Phase A1, Phase C1and Q2 causing a positive torque to be generated.

Step 5: Transistors Q5 and Q2 are conducting while Q1,3,4 and 6 arenon-conducting. Current flows from V_(cc) through Q5, Phase A1, Phase C1and Q2 causing a positive torque to be generated.

Step 6: Transistors Q5 and Q4 are conducting while Q1,2,3 and 6 arenon-conducting. Current flows from V_(cc) through Q5, Phase A1, Phase C1and Q4 causing a positive torque to be generated.

This sequence is used 6 times per revolution.

Unipolar Mode

Step 1: Transistors Q1 and Q16 are conducting while Q3 and 5 arenon-conducting. Current flows from V_(cc) through Q1, Phase A1,A2, PhaseB1,B2 and Q16 causing a positive torque to be generated.

Step 2: Transistors Q5 and Q16 are conducting while Q1 and 3 arenon-conducting. Current flows from V_(cc) through Q5, Phase A1,A2, PhaseC1,C2 and Q16 causing a positive torque to be generated.

Step 3: Transistors Q3 and Q16 are conducting while Q1 and 5 arenon-conducting. Current flows from V_(cc) through Q3, Phase A1,A2, PhaseC1,C2 and Q16 causing a positive torque to be generated.

This sequence is repeated six times per revolution.

Power Down Unload Mode

During power down with the disk spinning and the data still on the disk,the spindle motor must furnish the power to drive the actuator whichunloads the heads.

Transistor Q1,2,3,4,5,6,7,8,10,11,13,14,16 are turned off by the powerdown detection circuitry. Transistors Q9,12,15 are turned on so thatPhase A1,A2 are in series, B1,B2 are in series and C1,C2 are in seriesso that a greater back EMF voltage is generated than is possible withsingle winding (because of headroom considerations). Diodes D1,2,3,4,5and 6 form a fullwave bridge rectifier. The full potential of therectified voltage appears at the cathodes of D2,4, and 6. Q17 and 18 arealso turned on and the rectified voltage is applied to the actuator,which causes the heads to unload from the disk.

A better appreciation of the construction of the load beams utilized inthe dynamic head load version and the contact short stop versions of thedrives of the present invention would be obtained by reference to FIGS.6A-6L. Referring to FIG. 6A, load beam 14-1 is shown in plan view withthe underside, that is the side on which the read/write recordingtransducer will be mounted, facing upward in this figure. Load beam 14-1is referred to as the down load beam. Load beam 14-1 is unitary inconstruction and is preferably made from Type 302 non-magnetic stainlesssteel, having a thickness of approximately 0.0025 inches. As illustratedin FIG. 6A, load beam 14-1 includes load tab 17 which is semicircular incross section at its free end 80 as will be appreciated by reference toFIGS. 6C-2 and 6C". FIG. 6B illustrates load beam 14-1 in a side viewtaken along lines 6B--6B of FIG. 6A. In the view of FIG. 6B, the loadbeam 14-1 is shown in a flat and unloaded orientation. Tabs, denominated76, are utilized to secure the electrical wiring which extends to thefree end of the load beam for connection to the read/write transducerhead to be mounted at that location. The cross-section of load beam 14-1taken along lines 6E--6E is illustrated in FIG. 6E. The hat-shapedconfiguration of load beam 14-1 illustrated in FIG. 6E providesstiffening to the load beam. The configuration of load beam 14-1 changesfrom a generally flat orientation (with the exception of tabs 76 andstiffening channels 83 along the outer edge of the load beam) as shownin FIG. 6F, the cross-section taken along lines 6F--6F, to theconfiguration illustrated in FIG. 6E, and near the free end of load beam14-1 the load tab 17 is generally semi-circular as is illustrated inFIG. 6C which shows the view of load beam 14-1 taken along the line6C--6C in FIG. 6A. As will be appreciated by a reference to FIG. 6A, thecenter line of load beam 14-1 is at the position indicated by the dashedline denominated 77. It will also be appreciated by reference to FIG. 6Athat the curved end portion of lift tab 17 is not symmetrical withrespect to center line 77. This is also further illustrated in FIG. 6Cwhere the center line of load beam 14-1 is indicated by dashed linedenominated 77. The lowest point on lift tab 17 as measured from thecenter of radius 78-1 is indicated in FIG. 6C by reference line 78 whichextends to the lower surface 79 of lift tab 17.

A better appreciation of the offset relationship between the free end ofload tab 17 and the centerline 77 of down load beam 14-1 will beobtained by reference to FIGS. 6C-1 and 6C-2. FIG. 6C-1 is a top planview of down load 14-1 showing the end portion thereof and a portion offlexure 84. For simplicity, cam assembly 18 and disk 10 are not shown inFIG. 6C-1. In FIG. 6C-2, which is a view taken along 6C-2--6C-2, it willbe appreciated that the centerline 77 of lift beam 14-1 is to the leftof the lowest point of tab 17 (indicated by 78) to provide an offsetdistance 77/78. The free end of load tab 17 is offset toward the centerof disk 10 to provide symmetrical lifting of load beam 14-1 as itcontacts cam surface 18-2 In FIG. 6C", load tab 17 is illustrated at theposition where first contact is made with cam surface 18-2. The amountof the offset 77/78 is determined based on the angular slope θ, which ismeasured between cam surface 18-2 and surface 10' of disk 10, along withthe radius of lift tab 17, the radius being measured from center ofradius 78-1 and the lower surface 79. The lowest point of tab 17 isindicated at 78. The centerline offset may be calculated by the formula

    Centerline Offset=R sine θ

where

θ=angle between disk surface and cam surface

R=radius of curvature of load tab contacting the cam surface

With this offset, the lifting force on load beam 14-1 will be appliedsymmetrically along the centerline of load beam 14-1. In the preferredembodiment, the angle θ is 12°, and the radius of lift tab 17 at thepoint of contact with cam surface 18-2 is 0.46 mm. This results inoffset 77/78 being 0.095 mm. Similarly, the up load beams have their tabends offset, also toward the center of the disk, thereby ensuring thatthe first surface of the load tab to contact its corresponding camsurface does so along the center line of the load beam. This centerlinecontact eliminates any twisting forces on the load beam.

Referring to FIG. 6D, a cross-sectional view taken along the line 6D--6Dof FIG. 6A, it will be appreciated that the free end 80 of load 17 isoffset downwardly (with respect to the surface of the disk with whichthe load beam interfaces) from the plane of the flat surface of loadbeam 14-1 indicated by reference character 81 in FIG. 6D. This offset isprovided to maximize the clearance between load beams when theread/write heads are unloaded. Referring to FIG. 6G, swage plate is 82illustrated. Swage plate 82 is utilized in connecting the load beam tothe actuator body. Also illustrated in FIG. 6G is flexure 84, only aportion of which is illustrated in this figure. Flexure 84, which ispreferably constructed from stainless steel having a thickness in therange of about 0.0015 inches to 0.002 inches, is utilized to support theread/write transducer head in a flexible manner below the underside ofits respective load beam. A perspective view of flexure 84 isillustrated in FIG. 6J.

A side view of load beam 14-1 with its swage plate 82 is illustrated inFIG. 6H which is a view taken along the lines 6H--6H in FIG. 6G. In FIG.6H the load beam, flexure and associated read/write transducer areillustrated in loaded position. FIG. 6I illustrates load beam 14-1 withassociated read/write transducer and flexure in the unloaded position.As illustrated in FIG. 6I, there is a normal downward positioning of thefree end of load beam 14-1 which is by bending load beam 14-1 to providea predetermined pre-tensioning.

Referring to FIG. 6K, load beam 63-1 with its associated read/writetransducer 5 and flexure 84 are illustrated in a plan view taken fromthe underside of load beam 63-1. Also illustrated in FIG. 6K is wiringleads 85 which extend within tubing 86 which is supported in place bytabs 76 along the edge of load beam 63-1 to provide electricalconnection to read/write transducer 5. Although not illustrated in thefigures for the dynamic load beam version, a similar wiring arrangementis utilized for that structure as well. A side view of load beam 63-1and its associated structure is illustrated in FIG. 6L which is takenalong the lines of 6L--6L in FIG. 6K. Load beam 63-1 is constructed ofthe same type of material and same thickness is that used for load beams14-1 and 14-2 in the dynamic head load version.

FIG. 7A is a combined electrical block diagram and partial structuraldiagram illustrating, from a circuit standpoint the drive and controllerelectronics included on printed circuit board 2, and in addition theread/write analog integrated circuit 21 which is included within theenclosure of hard disk drive 1 (FIG. 1). In FIG. 7A, rigid disk 10 isillustrated in conjunction with lamination portions 64 of spin motor 3.The spin-up and control of the drive of the spin motor is under theelectrical control of spin control and drivers circuitry 74, an expandedblock diagram of which is illustrated in FIG. 8. In the embodimentillustrated in FIG. 1, spin control circuitry 74 is included on circuitboard 2. As indicated above, spin control circuitry 74 may beimplemented using an Allegro MicroSystems, Inc., part no. ULM 8902denominated Three Phase Brushless DC Motor Drive With Back-EMF Sensing(illustrated in FIG. 8 in block diagram form). Alternatively, the spincontrol and drivers circuitry described in the above identified U.S.patent application Ser. No. 07/630,470 could be used to control anddrive the spin motor. As also noted above, an alternative spin motor andassociated drive circuit may be used.

In FIG. 7A, upper load beam 14-1 is illustrated as positioned over aread/write area of disk 10, positioning read/write transducer 5 to adesired, addressed track location. Electrical conductors in a cable (notshown) provide analog information from the read/write recording elementto read/write preamp 21, which in the present embodiment is located inbaseplate 6 (as illustrated in FIGS. 1, 3A and 3B). Read/write preamp 21may be implemented, for example, by a Silicon Systems Incorporated, ofTustin, Calif. part no. 32R2030, or equivalent amplifier. Read/writepreamp 21 provides the functions well known to those skilled in the artto facilitate the recording and playback of digital information from thesurface of rigid disk 10. Signals from read/write preamp 21 are providedto and received from read/write combined function circuit 87, which inthe present embodiment of FIG. 7A is included on circuit board 2.

FIG. 10 illustrates in functional block form the circuits included inread/write combined function circuit 87. Read/write combined functioncircuit 87 may be implemented by, for example, a National Semiconductorpart no. DP8491 denominated Hard Disk Data Path Electronics Circuit.

Control signals to actuator coil 45 of the rotary actuator control theposition of the read/write recording elements supported on theirrespective load beams. In the present embodiment, actuator driver andpower off unload circuit 88 (FIG. 7A) provides control signals toposition the read/write recording elements to the desired location. Adetailed block diagram of actuator driver and power off unload circuit88 is illustrated in FIG. 11. The portion of actuator driver and poweroff unload circuit 88 of FIG. 11 illustrated within dashed line denotedby reference character 15-1 may be implemented by, for example, AllegroMicroSystems, Inc., Worchester, Mass., part no. 8932, denominated as avoice coil motor driver. The control signal to actuator coil 45 isanalog and is provided by actuator driver and power off unload circuit88. Also, as is well known to those skilled in the art, the feedbacksignals from the embedded servo (which will be described hereinafter)are provided in analog form. The seek control signals issued by hostcomputing device 87 when the host computing device 89 desires that theread/write recording element be positioned over a designated track, areprovided in digital form. To convert the analog signals returned fromthe embedded servo loop to digital signals and to convert the digitalsignals required for addressing a particular track to analog signals,actuator A/D & D/A circuit 90 is utilized. A detailed block diagram ofthe circuitry utilized in actuator A/D & D/A circuit 90 is illustratedin FIG. 14. This circuit may be conveniently implemented utilizing agenerally available part from Analog Devices, Norwood, Mass., their partno. ADC 7773, which is denominated as a complete embedded servo frontend for hard disk drive.

Returning to FIG. 7A, disk controller 91 is coupled between read/writecombo circuit 71, data bus 92, RAM buffer 93, and also provides signalsto and receives signals from interface connector 39 (FIG. 1) forcommunication outside of the drive and controller electronics board 2.Disk controller 91 may be conveniently implemented using Cirrus Logic,Inc. of Milpitas, Calif., Integrated PC Disk and Controller part no.CL-SH 265. RAM buffer 93 may be any digital storage device having acapacity of 32K addressable storage locations, each of 8 bits in width,and is preferably for convenience a semiconductor type random accessmemory device.

Drive and controller electronics board 2 further includes microprocessor94 which is coupled to data bus 92, read only memory 95 and gate array96. Microprocessor 77 may be implemented by, for example, a Motorolamicroprocessor model no. 68HC11 or an Intel Corporation microprocessorpart no. 80C196, or similarly functional microprocessors from othersources. Read only memory 95 may be any suitable memory device having32,000 storage locations, each 8 bits wide, and in the presentimplementation, for reduction of size, is preferably a semiconductormemory device.

FIG. 13 is a block diagram of gate array 96 (which is used with spinmotor in prior application Ser. No. 07/630,110) illustrating the blocksutilized therein. A description of the operation of gate array 96 willfollow hereinafter. Gate array circuit 97 (FIG. 15) is utilized with theabove-described alternative spin motor.

An embedded servo system is utilized in hard disk drive 1 of the presentinvention, the embedded servo system being implemented with the use ofelectronics which is illustrated in FIG. 7A (which includes othercircuitry). As illustrated in FIG. 7A, rigid disk 10 includes aplurality of circular tracks, for example tracks 121-i and 121-(i+1). Ifboth sides of rigid disk 10 are used for data, corresponding tracks onthe disk surfaces are approximately cylindrically aligned. Each track issegmented into one or more sectors SCT-01, SCT-02, . . . , SCT-n byprerecorded information in embedded servo field regions 120-1 through120-n. Each servo field region 120-j, where j=1, 2, . . . , n, includesm concentric servo fields, where m is the number of concentric circulardata tracks on the disk, that is, one servo field in each data track atposition j (a total of nm servo fields per surface). The particularembedded servo system utilized with hard disk drives 1 or 4 may be ofthe type described in copending and commonly assigned U.S. patentapplication Ser. No. 07/630,475 describe above. Alternatively, the servosystem described in the above-described copending commonly assigned U.S.patent application Ser. No. 07/M-1785 may be utilized.

Attention is directed to FIG. 13, which is a block diagram of gate array96 of FIG. 7A. As will be appreciated by reference to FIGS. 7A and FIG.13, multiplexed low address and data bus 92 is coupled to gate array 96for the bidirectional flow of information between microprocessor 94 andgate array 96. Throughout the drawing figures, lines with arrows on bothends indicate that there is a bidirectional flow of information over thelines in contrast to lines with an arrow on a single end which indicatesthat information passes in the direction of the arrow only. As will alsobe appreciated by reference to FIGS. 7A and 13, address information isprovided from microprocessor 94 to gate array 96 as inputs to gate array96. In addition, gate array 96 provides information to and receivesinformation from other circuitry in FIG. 7A and for convenience forunderstanding lines entering and leaving gate array 96 in FIG. 13 havelabels adjacent thereto to indicate the circuitry from which or to whichthe line is coupled. Referring to FIG. 13, address latch 98 is coupledto multiplexed low address and data bus 92 from which it receives andholds the lower order address information received from multiplexed lowaddress and data bus 92. Address latch 98 receives an address strobefrom microprocessor 94 which establishes the timing when the address isvalid. All outputs from address latch 98 are provided over bus 99 toread only memory 95 and additionally low order address information isalso provided from address latch 98 to actuator A/D & D/A circuit 90.The low order address from address latch 98 is also provided to addressdecoder 100 over bus 101. Address latch 98 is equivalent to anyavailable 8 bit latch, such as a 74LS373 latch. Address decoder 100receives the high order address information from microprocessor 94 viabus 186. Address decoder 100 uses the external high order address bits,the latched low order address bits from address latch 98 and the timingsignal, denominated DATASTROBE, received over line 80 frommicroprocessor 94 to decode the address for the gate array registers aswell and for external chip select lines. More particularly, EXTERNALCHIP SELECTS signals are provided over line 187 to the serial portselect of read/write combined function circuit 87, the select port forspin control circuit 74, as well as for the chip select inputs toactuator A/D & D/A circuit 90. Internally within gate array 96 thedecoded address information is used to select memory mappedcontrol/status registers for all of the blocks in gate array 96. Addressdecoder 100 may take the form of a well known circuit such as a group74LS138 decoders.

Clock logic memory mapped register 188 generates all of the requiredclock signals for programmable low power timer circuit 189, programmableword length serial port 190, digital demodulator & Gray code addressseparator 191, pulse width modulated timer 192, pulse width modulatedtimer 193 and encoder/decoder 194. Crystal 195, which is providedexternally of gate array 96, is used to provide a stable frequency ofoscillation for clock logic memory mapped register 188. The memorymapped register portion of clock logic memory mapped register 188functions to insure that minimum power is used or dissipated by enablingonly the required clocks for the operation in progress at the time theclock signal is required.

Programmable low power timer circuit 189 generates timing signals whichare provided to read/write preamp 21, over line 106, a timing signal online 107 to read/write combined function circuit 87, a plurality oftiming signals (which will be fully described hereinafter) over bus 108to digital demodulator & Gray code address separator 191 and, a timingsignal over line 109 to integrity checks & address comparator 110.Digital demodulator & Gray code address separator 191 generates windowsfor the pulse detector included in read/write combined function circuit87, over bus 111. To aid in understanding the operation of the variouscircuits and timing windows, attention is directed to FIG. 12A whichillustrates the servo field utilized on the disk 10 in conjunction withthe servo system in U.S. patent application Ser. No. 07/630,475, alongwith FIG. 12B which illustrates the windows produced by programmable lowpower timer circuit 189 and FIG. 12C which illustrates the windowsproduced by digital demodulator & Gray code address separator 191. Aswill be appreciated by reference to FIGS. 12B and 12C, the timing of therespective windows have been illustrated in timed relationship to theservo field of FIG. 12A. A detailed description of the servo field inFIG. 12A along with the circuitry involved is found in U.S. patentapplication Ser. No. 07/630,475 referred to above and the explanationtherefore will not be repeated. As an aid to understanding the windowsgenerated by programmable low timers circuit 189 and digital demodulator& Gray code address separator 191, the following table is provided whichin the left hand column lists the window acronym designation illustratedin FIGS. 12B and 12C, in the center column provides a descriptive titlefor the windows function and in the far right column indicates thecircuit to which the window signal is provided.

                  TABLE                                                           ______________________________________                                        Window    Descriptive Function                                                                          Window Signal                                       Acronym   Of Window       Provided to                                         ______________________________________                                        RW.sub.-- ON                                                                            Read/write preamp                                                                             R/W Preamp 49 R/W                                             turned on       combo 71                                            PD.sub.-- ON                                                                            Pulse detector turned                                                                         R/W combo 71                                                  on                                                                  START.sub.-- SF                                                                         Start servo field                                                                             Digital Demodulator                                                           91 & Gray Code                                                                Address Separator                                   SRCH.sub.-- ON                                                                          Search for Gap and                                                                            Digital Demodulator                                           Sync            91 & Gray Code                                                                Address Separator                                   SRCH.sub.-- END                                                                         End search for Gap                                                                            Digital Demodulator                                           and Sync        91 & Gray Code                                                                Address Separator                                   NOM.sub.-- END                                                                          Nominal end of servo                                                                          Digital Demodulator                                           field           91 & Gray Code                                                                Address Separator                                   SVF.sub.-- Time                                                                         Servo field time                                                                              Read/Write Combo 71                                 SV.sub.-- WR.sub.-- EN                                                                  Servo write enable                                                                            Read/Write Combo 71                                 AGC.sub.-- HOLD                                                                         Hold gain of AGC                                                                              Read/Write Combo 71                                           during gap and                                                                position                                                            LOW.sub.-- THRS                                                                         Lower detection Read/Write Combo 71                                           threshold during Gray                                                         address field                                                       RESTART   Restart low power                                                                             To low power timers                                           timers                                                              ______________________________________                                    

Integrity checks & address comparator 110 compares the integrity checkpattern which is created from reading the servo field information (whichis described in detail from the above-referenced M-1470 U.S. patentapplication Serial No. 07/630,475) with the expected pattern stored in amemory mapped register in integrity check & address comparator 110. Inaddition, the track address is selectively compared with the expectedtrack address during track following (ON track MODE). If either of thesecomparisons do not match, an error condition stored in a status registeris assumed and is sent to microprocessor 94 over data line 112 as statusinformation.

Returning to digital demodulator & Gray code address separator 191 whichwas briefly referred to above, the output of this circuit is providedover bus 111 as windows for the pulse detector in read/write combo chip87. Digital demodulator & Gray code address separator 191 receives, overline 113, the transition pulse and polarity signals from read/writecombo chip 87. Using this information, digital demodulator & Gray codeaddress separator 191 determines the track address and provides thistrack address information to microprocessor 94, as well as to integritychecks & address comparator 110.

Pulse width modulated timer 192 has an input coupled to multiplexed lowaddress and data bus 92 through which the microprocessor programs thefrequency and the duty cycle of the output. This data is stored in twomemory registers which are included in pulse width modulated timer 192which generates at its output a control signal to set the level of theread threshold, this control signal being provided to read/writecombined function circuit 87 over line 123. Pulse width modulated timer193 also receives an input from multiplexed low address and data bus 92and provides at its output a write current control signal which isprovided to read/write analog circuit 21 over line 114. The outputs oftimers 192 and 193 are filtered by suitable RC networks (not shown) toprovide an appropriate voltage for the above two functions. The timeconstant of the RC network for the output of these two timers is afunction of the device being driven and is determined by well knowntechniques.

Programmable word length serial port 190 is utilized to programread/write combined function circuit 87, actuator driver 88 and spincontrol circuit 74. Serial clock output from programmable word lengthserial port 190 is also provided to each of the foregoing chips. Theprogramming information to be provided to read/write combined functioncircuit 87, actuator driver 88 and spin control and driver circuit 74 isloaded into programmable word length serial port 90 from microprocessor94 over multiplexed low address and data bus 92. The designated addressfor this programming is set by the microprocessor through addressdecoder 100, and the data contents and length is set by a microprocessorthrough the memory map register included in programmable word lengthserial port 190.

Power management circuit 119 is a memory mapped set of registers whichcontrols the activation of each functional block of the drive. Only theblocks requiring to be active at a given time are activated andtherefore the minimum overall power required by the drive is utilized.

Encoder/decoder 194 receives NRZ write data and clock signals from diskcontroller 91 and generates from these signals write code data which isprovided over line 120 to read/write combined function circuit 87.Encoder/decoder 194 receives RDGATE and WRGATE signals as enable signalsfrom disk controller 91. Encoder/decoder 194 receives read code data andclock signals from read/write combined function circuit 87 and generatesNRZ read data and NRZ read clock signals which are provided to diskcontroller 91 over lines 121 and 122 respectively. Encoder decodercircuit 194 may be implemented by using standard 1,7 encoding circuitrywell known to those skilled in the art.

FIG. 12D illustrates the servo field utilized in conjunction with theservo circuitry described and claimed in the above-identified U.S.patent application Ser. No. 07/765,348.

In the terminology used in the rigid disk drive and other computerperipheral storage device art, the term head disk assembly, alsosometimes abbreviated HDA, refers to the head and disk structures andother apparatus and circuitry included within the enclosure which housesthe head and disk mechanism. For example, in FIG. 1, the componentsincluded in the housing which is bounded on the lower side by base plate6 and on the upper side by top cover 26 be considered the HDA for harddisk drive 1. An advantage to housing circuitry within the HDA is thatsince the base plate and top cover are both electrically conductive,there is a sealed housing which prevents external electricalinterference from entering the housing and affecting circuitry withinthe HDA. External electrical interference is normally only a problemwith circuits and conductors which carry analog signals. It has beendiscovered that a very advantageous disk drive system can be constructedby including within the HDA all of the analog circuitry and signallines, while including exterior of the HDA signal lines and circuitswhich process only digital information. Digital circuitry could ofcourse also be included within the HDA housing, however doing so mayresult in a size penalty for the HDA which may not be desirable.Referring to FIG. 7B, an embodiment of the present invention isdisclosed in which the above-identified advantageous result of reducedinterference to electrical signals in the system is achieved. In FIG.7b, the dashed line indicated by reference character 125 demarks theabove-described separation of the analog and digital circuitry foraccomplishing the separation to provide the advantageous result ofreduced susceptibility to noise interference from external sources. Asit will be appreciated by, referring to FIG. 7B, the circuitry to theright of, and below, line 125 process analog signals and converts theminto digital form before those signals are sent to the circuitry in theblocks to the left of line 125. More particularly, the read/write preamp21, read/write combined function circuit 87, actuator driver and poweroff unload circuit 88, spin control and driver circuitry 74 and theactuator A/D and D/A circuitry 90 all process analog data, however theanalog data is converted into digital data before that data istransferred to the other circuit blocks within the disk drive system.Structurally, implementing the invention described above is achieved byplacing the aforementioned analog circuitry within the HDA housing andsending to the exterior of the housing via suitable connectors digitalinformation to the remaining portions of the system. In this manner,only digital information is transferred from the interior of the HDA tothe outside circuitry and any electrical interference which may bepresent in the area would be less likely to affect the digital signalssince they are less susceptible electrical noise than other types ofsignals.

As mentioned previously, the gate array circuitry utilized with thepresent invention is a function of which spin control and drivercircuit, and which spin control motor previously described will beutilized in the drive. FIG. 15 illustrates gate array 97, in high levelblock diagram form, which is utilized with the spin motor and drivecircuitry discussed above with respect to spin motor drive circuit 75and the modified spin motor described in connection therewith. Internaldecoder circuitry 151 receives address and data signals frommicroprocessor 94. Internal decoder circuitry 151 contains the memorymap for the entire system as well as address latches and data read orwrite state. The address may map to an internal, on-chip, function ormay be an external location. A digital decoder determines the routingand sends all external address commands out to either the address anddata lines output multiplex circuitry 161 or output control lines 162.

Peripheral chip control circuitry 152 receives commands from inputcontrol lines 163 (connections not illustrated in the figure) orinternally written ASIC registers and sends commands to output controllines 162 (connections not illustrated in the figure) to control theread/write integrated circuit 21 in the HDA. Serial communication portcircuitry 153 is similar in operation to an RS-232 interface. It is usedto load other chips with serial data from microprocessor 94, such as thefrequency synthesizer, D/A converter, R/W pulse detector and filter usedin the encoder decoder logic. Signals from this port appear at outputcontrol lines 162.

Spin control circuitry 154 selects the spin motor logic control clockfrom either the external spin motor generated clock or an internallygenerated clock derived from sector pulses. The output clock is placedon output control lines 162. Encode decode circuitry 155 providesencoding and decoding of the 1,7:2,3 coded read/write data signals fromthe input control lines 163 to the output control lines 162.

PWM control ports circuitry 156 generates three pulse-width modulatedbit streams which are placed on output control lines 162. The firstsignal is used to control the magnetic head write current, the second tocontrol the read channel amplitude threshold and the third to controlthe spin motor voltage.

Servo sequencer circuitry 157 reads the track position servoinformation. It acts to detect index and cylinder address informationand derives timing signals from the synchronization signals, and furthersteers analog position information to the peak detection circuitry toobtain exact position information. Information is received from inputcontrol lines 163 and after processing appears at output control lines162.

Clock generation and control circuitry 158 enables and disables thecrystal oscillator (not shown) which is connected to clock generationand control circuitry 158. Programmable dividers provide variable clocksignals for spin motor control, buffer control and frequencysynthesizing.

Address trigger circuitry 159 is comprised of a programmable 16 bitregister and digital comparator which examines address information fromthe internal decoder circuitry 151 and can be used for diagnosticpurposes. Output signals appear at output control lines 162.

Internal registers 160 are used to store index address, cylinderaddress, status information and bit mapped error codes from the servosequencer and to drive the peripheral control lines. Output multiplexcircuitry 161 allows internal data registers and input control lines tobe read by the microprocessor.

We claim:
 1. A disk drive information storage device comprising:ahousing having a footprint that includes a first dimension of about 35mm; a substantially rigid disk supported by said housing for rotation;an elongated actuator arm including a load beam, said actuator arm beingpivotally supported by said housing about a center of rotation, forrotation of one end of said load beam in a plane substantially parallelto a surface of said disk, said load beam including at its outermost enda lift tab, said lift tab being positioned such that a centerline ofsaid lift tab is offset from a centerline of said load beam; a sliderbody including a read/write recording element; means connected to saidload beam and said slider body for supporting said slider body at aposition intermediate said center of rotation and said lift tab; and acam assembly supported by said housing adjacent to said lift tab and theedge of said disk, said cam assembly including a cam surface positionedin operative relationship with said lift tab, said lift tab contactingsaid cam surface and in cooperation with said cam surface providing alifting force along the centerline of said load beam.
 2. A disk driveinformation storage device according to claim 1, further comprising aspin motor for driving said disk to rotate said disk, wherein said spinmotor is operable from a supply voltage in the range of from about 3volts to about 5 volts.
 3. A disk drive information storage deviceaccording to claim 1, further comprising a ferrite shield membersupported in said housing adjacent to said slider body for shieldingsaid read/write recording element from electrical noise.
 4. A disk driveinformation storage device according to claim 1, wherein said sliderbody is the 50% size.
 5. A disk drive information storage deviceaccording to claim 1 further comprising a spin motor for rotating saiddisk, said spin motor including a plurality of poles, and wherein thenumber of poles is greater than twelve.
 6. A disk drive informationstorage device according to claim 1, wherein said disk has a diameter inthe range of from about 33 mm to about 34 mm.
 7. A disk driveinformation storage device according to claim 6, wherein said footprintincludes a second dimension of about 50.8 mm.
 8. A disk driveinformation storage device according to claim 1, wherein said footprintincludes a second dimension of about 50.8 mm.
 9. A disk driveinformation storage device comprising:a housing; a substantially rigiddisk supported by said housing for rotation, said disk having a diameterin the range of about 33 mm to about 34 mm; an elongated actuator armincluding a load beam, said actuator arm being pivotally supported bysaid housing about a center of rotation, for rotation of one end of saidload beam in a plane substantially parallel to a surface of said disk,said load beam including at its outermost end a lift tab, said lift tabbeing positioned such that a centerline of said lift tab is offset froma centerline of said load beam; a slider body including a read/writerecording element; means connected to said load beam and said sliderbody for supporting said slider body at a position intermediate saidcenter of rotation and said lift tab; and a cam assembly supported bysaid housing adjacent to said lift tab and the edge of said disk, saidcam assembly including a cam surface positioned in operativerelationship with said lift tab, said lift tab contacting said camsurface and in cooperation with said cam surface providing a liftingforce along the centerline of said load beam.
 10. A disk driveinformation storage device according to claim 9, further comprising aspin motor for driving a said disk to rotate said disk, wherein saidspin motor is operable from a supply voltage in the range of from about3 volts to about 5 volts.
 11. A disk drive information storage deviceaccording to claim 9, further comprising a ferrite shield membersupported in said housing adjacent to said slider body for shieldingsaid read/write recording element from electrical noise.
 12. A diskdrive information storage device according to claim 9, wherein saidslider body is of the 50% size.
 13. A disk drive information storagedevice according to claim 9, further comprising a spin motor forrotating said disk, said spin motor including a plurality of poles, andwherein the number of poles is greater than twelve.